RADIODYNAMICS 

THE   WIRELESS    CONTROL   OF   TORPEDOES 
AND   OTHER   MECHANISMS 


BY 


B.  F.  MIESSNER 

Associate  Member  Institute  of  Radio  Engineers, 
Expert  Radio  Aide,  U.  S.  Navy 


112  ILLUSTRATIONS 


NEW  YORK 

D.    VAN    NOSTRAND    COMPANY 

25   PARK   PLACE 

1916 


COPYRIGHT*  1916. 

BY 
D.  VAN  NOSTRAND   COMPANY 


Stanbopc  flbreas 

F.    H.GILSON   COMPANY 
BOSTON,  U.S.A. 


PREFACE 


IN  the  preparation  of  this  work  the  author  has  endeavored 
to  present  in  an  orderly  and  instructive  fashion  the  most 
important  material  concerning  the  history,  methods  and 
apparatus  of  Radiodynamics,  the  art  of  controlling  distant 
mechanisms  without  artificial  connecting  means. 

He  has  aimed  especially  at  a  treatment  of  his  subject-matter 
that  would  be  intelligible  to  the  general  reader  without  sacri- 
ficing the  technical  exactitude  which  makes  scientific  work  of 
value  to  the  trained  engineer. 

The  chief  recent  developments  in  this  new  art  have  been 
of  a  military  nature,  and  for  this  reason  the  volume  is  devoted 
for  the  most  part  to  the  torpedo-control  applications  of 
Radiodynamics. 

It  is  hoped  that  the  book  may  prove  interesting  to  the  gen- 
eral scientific  reader,  as  well  as  to  the  trained  engineer,  and 
to  those  concerned  in  the  purely  military  applications  and 
possibilities  of  wirelessly-controlled  mechanisms. 

The  author  desires  here  to  thank  the  many  friends  who 
have  generously  assisted  him  in  collecting  his  materials.  He 
desires  especially  to  express  his  obligation  to  Professor  M.  H. 
Liddell,  of  Purdue  University  for  his  advice  and  assistance  in 
the  preparation  of  the  book  for  press. 

B.  F.  M. 

LAFAYETTE,  IND., 
August,  1916. 


in 


O  o  n  /t  *t  o 


CONTENTS 

CHAPTER  PAGE 

I.  HISTORICAL i 

i — IT.  WIRELESS  CONTROL  OF  MECHANISMS 6 

III.  PRACTICAL  WIRELESS  TELEGRAPHY 12 

IV.  ELECTROSTATIC  AND  COMBINED  INDUCTION  —  CONDUCTION  TELE- 

GRAPH SYSTEMS 19 

V.  ELECTROMAGNETIC  WAVE  SYSTEMS 27 

VI.  POSSIBLE    CONTROL    METHODS    FOR    RADIODYNAMICS  —  SOUND 

WAVES 33 

VII.  INFRA-RED  OR  HEAT  WAVES 41 

VIII.  VISIBLE  AND  ULTRA-VIOLET  WAVES 57 

IX.  EARTH  CONDUCTION 67 

X.  ELECTROSTATIC  AND  ELECTROMAGNETIC  INDUCTION  —  HERTZIAN 

WAVES 74 

XI.  THE  ADVENT  OF  WIRELESSLY  CONTROLLED  TORPEDOES 78 

XII.   SELECTORS 89 

XIII.  EUROPEAN  CONTROL  SYSTEMS •. 92 

XIV.  WORK  OF  THE  HAMMOND  RADIO  RESEARCH  LABORATORY 107 

XV.  THE  SOLUTION  OF  THE  PROBLEMS  RELATED  TO  BATTLE-RANGE 

TORPEDO  CONTROL 124 

XVI.  THE  DIFFICULTIES   ENCOUNTERED  IN   PROVIDING   PROTECTION 

FROM  INTERFERENCE 137 

XVII.  A  MEANS  OF  OBTAINING  SELECTIVITY 145 

XVIII.  NATURE  OF  INDICATOR  CURRENTS  IN  RADIO  RECEIVERS 150 

XIX.  THE  INTERFERENCE  PREVENTER 159 

XX.  DETECTORS 167 

XXI.  METHODS  OF  INCREASING  RECEIVED  EFFECTS 175 

XXII.  RELAYS 180 

XXIII.  TORPEDO  ANTENNAE 183 

XXIV.  RECENT  DEVELOPMENTS.  .  .  188 


RADIODYNAMICS 


CHAPTER   I 
HISTORICAL 

From  earliest  times  methods  of  conveying  intelligence  to  a 
distance  have  been  universally  known  and  utilized.  Fleet- 
footed  runners,  fires  and  torches  by  night,  and  smoke  by  day 
as  well  as  acoustic  methods  using  both  air  and  earth  as  con- 
ducting mediums  seem  to  have  been  among  the  first  means  of 
comparatively  distant  signalling.  We  read  of  them  in  the 
Bible  (Jeremiah)  and  in  the  Greek  and  Latin  authors;  their 
use  in  the  far  East  and  in  Europe  leaves  no  doubt  as  to  their 
wide  employment  amongst  civilized  nations. 

The  Indians  of  America  from  the  North  to  Cape  Horn  still 
use  lighted  fires  and  blanket-controlled  smoke  clouds  to  an- 
nounce special  tidings  and  convey  important  messages;  their 
system  of  optical  signalling  in  which  the  arms  were  used, 
furnished  the  basis  for  the  semaphore,  which  toward  the  end 
of  the  eighteenth  century  came  into  general  use  in  Europe. 
It  may  still  be  seen  on  any  railroad.  The  semaphore  system 
was  still  further  elaborated  for  maritime  and  military  pur- 
poses and  today  in  the  armies  and  navies  of  the  world  we 
have  semaphore  and  flag  signalling  as  a  very  important  means 
of  communicating  intelligence  to  distances  not  in  excess  of  a 
few  miles.  The  heliograph  by  day  and  the  electric  search- 
light by  day  and  night  can  both  trace  their  evolution  to  the 
primeval  fire  and  torch. 


$,  ;  I/I  y  £  *  ^  RApIODYNAMICS 

The  application  of  electricity  has  revolutionized  all  pre- 
vious methods  of  signalling.  The  phenomenon  of  attraction 
was  well  known  to  the  ancients.  Thales,  the  founder  of 
Ionic  philosophy,  who  lived  six  hundred  years  before  Christ, 
noticed  the  effects  of  friction  on  amber,  and  Theophrastus, 
Pliny  and  other  writers  recorded  similar  phenomena. 

In  1727  Stephen  Gray,  a  pensioner  of  the  Charter  House, 
London,  made  an  electric  discharge  pass  over  a  circuit  of 
700  feet.  Shortly  after  the  discovery  of  the  Leyden  jar  by 
Muschenbroek  of  Leyden,  in  1746,  Dr.  Watson,  a  bishop  of 
Llandaff,  transmitted  a  charge  through  2800  feet  of  wire. 
In  the  same  year  he  increased  the  distance  of  transmission  to 
10,600  feet  through  wires  stretched  on  poles  erected  on 
Shooter's  Hill,  London.  Benjamin  Franklin  made  similar  ex- 
periments in  1748  over  the  Schuylkill  river  at  Philadelphia. 
Le  Sage  of  Geneva  established  the  first  telegraph  system  for 
the  transmission  of  intelligible  signals  in  1774*;  this  system 
was  based  on  electrostatic  action.  The  next  important  law 
was  discovered  by  Romagnesi  of  Trente  in  1805;  but  at- 
tracted little  attention  until  it  was  rediscovered  in  1819  by 
Oersted.  This  discovery  showed  that  a  current-carrying  wire 
is  able  to  deflect  a  magnetic  needle.  Schweigger  in  1820 
discovered  that  the  deflecting  force  was  increased  by  winding 
the  wire  several  times  around  the  needle.  These  very  im- 
portant discoveries  paved  the  way  for  the  galvanoscope  and 
galvanometer.  Galvanoscopic  or  needle  telegraphs  were  sub- 
sequently evolved. 

In  1832  Schilling,  a  Russian,  devised  a  single-needle  tele- 
graph using  reverse  currents  and  combinations  of  signals  for 
an  alphabet.  Schilling's  telegraph  was  developed  by  Gauss 
and  Weber,  who  built  a  line  three  miles  long  at  Gottingen. 

While  Prof.  A.  C.  Steinheil  of  Munich  was  establishing  a 
system  of  telegraphy  in  Bavaria,  Gauss,  the  celebrated  German 
*  Moigno's  "  T616graphie  Electrique,"  p.  59. 


HISTORICAL  3 

philosopher  and  himself  a  telegraph  inventor,  suggested  to 
him  that  the  two  rails  of  a  railway  might  be  used  as  telegraph 
conductors.  In  July,  1838,  Steinheil  tried  the  experiment  on 
the  Nurmberg-Furth  railway,  but  was  unable  to  obtain  an 
insulation  of  the  rails  sufficiently  good  for  the  current  to 
reach  from  one  station  to  the  other.  The  great  conductiv- 
ity with  which  he  found  that  the  earth  was  endowed  led 
him  to  presume  that  it  would  be  possible  to  employ  it  instead 
of  the  return  wire  or  wires  hitherto  used.  The  trials  that  he 
made  in  order  to  prove  the  accuracy  of  this  conclusion  were 
followed  by  complete  success,  and  he  then  introduced  into 
electric  telegraphy  one  of  its  greatest  improvements  —  the 
earth  return  circuit.-* 

Following  Sturgeon's  invention  of  the  electromagnet  in 
1825  and  the  simultaneous  discovery  by  Faraday  in  England 
and  Henry  in  America  (1831)  of  the  laws  of  electromagnetic 
induction,  Morse  laid  the  foundations  in  1836  of  the  present 
overland  electromagnetic  telegraph  system.  In  the  same 
year  in  England  Wheatstone  with  W.  F.  Cooke  still  further 
perfected  the  needle  telegraph  and  a  year  later  put  a  crude 
system  of  telegraphy  into  actual  service  on  the  London  and 
Black  well  Railway.  In  1839  the  first  public  line  was  opened 
by  Wheatstone  between  Paddington  and  Slough,  England, 
twenty  miles  of  goose  quills  being  used  for  insulation. 

It  was  once  supposed  that  Wheatstone  was  the  original 
inventor  of  the  electric  telegraph,  but  strictly  speaking  it  had 
no  inventor;  it  is  rather  the  result  of  accumulated  discoveries 
each  adding  its  quota  to  advance  the  invention  towards  per- 
fection. The  greatest  achievement  of  Wheatstone  was  his 
automatic,  recording  telegraph,  which  is  extensively  used  for 
press  and  other  long  dispatches  and  which  has  attained 
marvelous  speeds  for  a  mechanical  recorder. 

*  For  an  account  of  the  earth  return  before  1838  see  Fahie's  "History  of 
Electric  Telegraphy  to  the  Year  1837,"  pp.  343-348. 


4  RADIODYNAMICS 

Morse  constructed  his  electromagnetic  telegraph  in  1836, 
and  in  the  next  few  years  he  devised  many  important  modi- 
fications. Congress  made  him  an  appropriation  of  $30,000  in 
March,  1843,  and  on  the  24th  of  March,  1844,  the  first  tele- 
graph line  in  the  United  States  was  successfully  opened  between 
Washington  and  Baltimore,  a  distance  of  about  40  miles. 

The  electrostatic  telegraph  of  Le  Sage  was  probably  the 
first  instance  of  the  control  of  mechanisms  from  a  distance 
by  the  use  of  conducting  wires.  The  real  art  of  teledy- 
namics,*  however,  is  based  on  the  discoveries  by  Romagnesi, 
Oersted,  and  Schweigger  of  the  phenomena  of  electromagnet- 
ism  which  led  up  to  the  conception  and  development  of  the 
electromagnetic  telegraph.  Since  1836,  when  Morse  con- 
structed his  first  telegraph,  no  very  radical  changes  have  been 
made  in  the  general  scheme  on  which  his  system  was  based, 
but  it  has  been  gradually  and  surely  developed  and  brought  to 
the  present  stage  of  perfection.  One  very  conspicuous  change 
in  detail,  however,  is  worthy  of  mention.  The  electromagnetic 
sounder  first  used  by  Morse  on  the  line  between  Washington 
and  Baltimore  and  exhibited  in  the  National  Museum  in 
Washington  weighed  one  hundred  eighty-five  pounds.  The 
arms  were  three  and  one-half  inches  in  diameter  and  eighteen 
inches  long,  the  same  size  of  copper  wire  being  used  for  the 
coils  as  for  the  line  wire.  It  was  then  supposed  that  the 
wire  of  the  coils  and  of  the  line  should  be  of  the  same  size 
throughout,  and  even  down  to  1860  many  practical  telegraph- 
ers held  this  view.f  The  sounders  now  used  weigh  about 
one  pound  and  require  no  more  than  about  seventy-five 
cubic  inches  of  space.  The  coils  are  wound  with  wire  much 
smaller  than  the  line  wire,  a  great  increase  in  sensitiveness 
being  thereby  produced. 

*  The  art  of  controlling  mechanisms  from  a  distance;  as  used  here  it  refers 
only  to  distant  control,  by  electrical  means,  with  or  without  connecting  wires, 
t  London  Electrical  Review,  Aug.  9,  1895,  p.  157. 


HISTORICAL  5 

The  necessity  for  long-distance  telegraphy  brought  about 
the  invention  of  the  relay,  a  very  sensitive  form  of  sounder 
which  is  actuated  by  the  weak  line  currents  and  which  in 
turn  controls  the  current  for  operating  the  sounder  used  in 
receiving  messages.  The  relay  is  a  very  important  part  of 
all  systems  for  the  distant  control  of  mechanisms  as  by  its 
use  practically  any  amount  of  power  can  be  controlled.  The 
mere  pressure  of  the  finger  on  a  telegraph  key  through  which 
a  few  thousandths  of  an  ampere  flow  to  a  distant  relay  is 
sufficient  to  start  or  stop  the  most  powerful  machinery  or  to 
set  off  explosive  charges  strong  enough  to  destroy  a  whole 
city. 

Such  mechanisms  as  electric  bells  and  signals  of  various 
kinds,  telephone  and  fire  alarm  systems,  electric  clocks  and 
chimes,  and  time  distribution  systems  are  all  developments 
in  the  art  of  teledynamics.  Present-day  automatic  tele- 
phone systems,  the  distant  control  of  searchlights,  and  the 
wire-controlled  torpedo  are  examples  of  the  wonderful  possi- 
bilities along  these  lines. 


CHAPTER   II 
WIRELESS    CONTROL   OF   MECHANISMS 

Like  most  wonderful  inventions  the  telegraphic  transmission 
of  signals  without  the  aid  of  conducting  wires  is  in  reality 
not  an  invention,  according  to  the  popular  conception  of  the 
word,  but  rather  the  result  of  the  combined  efforts  of  many 
deep-thinking  scientific  men  extending  over  a  period  of  many 
years.  After  the  discovery  of  the  galvanic  current  and  elec- 
tromagnetism  in  the  seventeenth  and  eighteenth  centuries 
the  conception  and  development  of  wireless  telegraphy  and 
wire  telegraphy  occurred  at  practically  the  same  time.  It 
was  in  1836  that  Morse  constructed  his  first  telegraph;  this 
was  not  put  into  practical  operation  until  1844.  In  I^38 
Steinheil  of  Munich,  one  of  the  great  pioneers  of  electric 
telegraphy  in  Europe,  gave  the  first  intelligent*  suggestion 
of  a  wireless  telegraph.  In  a  paper  on  this  subject  Steinheil, 
explaining  his  theories  and  observations  on  earth  conduction 
telegraphy,  says: 

"The  inquiry  into  the  laws  of  dispersion  according  to  which 
the  ground,  whose  mass  is  unlimited,  is  acted  upon  by  the 
passage  of  a  galvanic  current  appeared  to  be  a  subject  replete 
with  interest.  The  galvanic  excitation  cannot  be  confined 

*  Earlier  but  vague  and  impractical  suggestions  were  made  previous  to  this 
time.  In  the  Bible  we  find:  "  Canst  thou  send  lightnings,  that  they  may  go, 
and  say  unto  thee,  '  Here  we  are  ?  ": 

In  1632  Galileo  wrote  of  a  secret  art  by  which  it  would  be  possible  to  con- 
verse across  a  space  of  several  thousand  miles  through  the  attraction  of  a 
magnetic  needle  ("Galilei  Systema  Cosmicum."  Dial.  I).  The  "Prolusiones 
Academicae"  of  Strada,  which  was  published  in  1617,  described  a  method  of 
communicating  at  a  distance  by  means  of  two  pivoted  magnetic  needles. 

6 


WIRELESS   CONTROL   OF  MECHANISMS  7 

to  the  portions  of  earth  situated  between  the  two  ends  of  the 
wire;  on  the  contrary  it  cannot  but  extend  itself  indefinitely 
and  it  therefore  only  depends  on  the  law  that  obtains  in  this 
excitation  of  the  ground,  and  the  distance  of  the  exciting  ter- 
minations of  the  wire,  whether  it  is  necessary  or  not  to  have 
any  metallic  communication  at  all  for  carrying  on  telegraphic 
intercourse. 

"An  apparatus  can  it  is  true  be  constructed  in  which  the 
inductor,  having  no  other  metallic  connection  with  the 
multiplier  than  the  excitation  transmitted  through  the  ground, 
shall  produce  galvanic  currents  in  that  multiplier  sufficient 
to  cause  a  visible  deflection  of  the  bar.  This  is  a  hitherto 
unobserved  fact  and  may  be  classed  amongst  the  most  ex- 
traordinary phenomena  that  science  has  revealed  to  us.  It 
only  holds  good,  however,  for  small  distances;  and  it  must  be 
left  to  the  future  to  decide  whether  we  shall  ever  succeed  in 
telegraphing  at  great  distances  without  any  metallic  con- 
nection at  all.  My  experiments  prove  that  such  a  thing  is 
possible  up  to  distances  of  fifty  feet.  For  greater  distances 
we  can  only  conceive  it  feasible  by  augmenting  the  power  of 
the  galvanic  induction,  or  by  appropriate  multipliers  con- 
structed for  the  purpose,  or,  in  conclusion,  by  increasing  the 
surface  of  contact  presented  by  the  ends  of  the  multipliers. 
At  all  events  the  phenomenon  merits  our  best  attention,  and 
its  influence  will  not  perhaps  be  altogether  overlooked  in  the 
theoretic  views  we  may  form  with  regard  to  galvanism 
itself."  * 

Discussing  the  same  subject  in  another  publication  Stein- 
heil  says:  "We  cannot  conjure  up  gnomes  at  will  to  convey 
our  thoughts  through  the  earth,  Nature  has  prevented  this. 
The  spreading  of  the  galvanic  effect  is  proportional  not  to 
the  distance  of  the  point  of  excitation  but  to  the  square  of 
this  distance;  so  that  at  the  distance  of  fifty  feet  only  ex- 
*  Sturgeon's  "Annals  of  Electricity,"  vol.  in,  p.  450. 


8  RADIODYNAMICS 

ceedingly  small  effects  can  be  produced  by  the  most  powerful 
electrical  effect  at  the  point  of  excitation.  Had  we  means 
which  could  stand  in  the  same  relation  to  electricity  as  the 
eye  stands  to  light  nothing  would  prevent  our  telegraphing 
through  the  earth  without  conducting  wires;  but  it  is  not 
probable  that  we  shall  ever  attain  this  end."  * 

Steinheil  apparently  received  his  inspiration  for  this  method 
of  transmitting  signals  from  his  accidental  discovery  of  the 
conductivity  of  the  earth  in  the  experiments  on  the  Nurm- 
berg-Fiirth  railroad.  His  explanation,  which  is  somewhat 
nebulous  and  obscured  by  such  expressions  as  "multipliers," 


\  \ 


^  \ 

----  "        /rth* 


FIG.  i. 

"  galvanic  excitation,"  and  "galvanic  induction,"  actually 
amounts  to  this:  When  two  earthed  conducting  plates  are 
connected  to  an  electric  battery,  current  flows  through  the 
earth,  but  not  wholly  through  that  portion  directly  between 
the  plates.  Instead,  the  current  obeys  Ohm's  law  with  re- 
gard to  a  circuit  including  conductors  in  parallel,  i.e.,  the 
current  in  any  branch  is  inversely  proportional  to  its  resist- 
ance. The  number  of  parallel  branches  in  the  earth  circuit 
is  infinite,  but  they  obey  this  same  law.  The  earth  between 
the  buried  plates,  although  having  a  high  specific  resistance, 
has  a  very  great  cross  sectional  area;  this  accounts  for  the 
relatively  low  resistance  of  earth  returns.  The  current 

*  The  electric  eye  of  Hertz!    "Die  Anwendung  des  Electromagnetismus," 
1873,  p.  172. 


WIRELESS  CONTROL  OF  MECHANISMS  9 

density,  according  to  Ohm's  law  is  greatest  between  the 
plates,  and  decreases  in  proportion  to  the  distance  along  any 
line  at  right  angles  to  the  line  joining  the  plates.  This  is 
shown  in  Fig.  i. 

SteinheiPs  scheme  was  to  so  place  another  set  of  earth  plates 
connected  by  a  wire  and  current  indicator  that  the  current 

would  traverse  the  earth  between  ^ 

the  sending  and  receiving  plates,        C~  "~"| 

as   shown   in   Fig.  2,  and  thus     — *— y  .y**' — 

operate  the  receiving  instrument.        I       \Earth  p/ates  < 

Steinheil's  inability  to  signal    t       x'  %X 

over  distances  greater  than  fifty        I J 

feet  was,  no  doubt,  due  to  the  '^7*^  indicator 

limited  capacity  of  his  current  FIG   2 

supply,  the  insensitiveness  of  his 

receiving  indicator,  and  his  probable  ignorance  of  the  fact  that 

the  distance  between  the  transmitting  plates  should  be  at  least 

three  times  the  distance  to  be  bridged,  for  the  best  results. 

Another  means  of  signalling  without  connecting  wires  was 
disclosed  by  Steinheil  in  a  classic  paper  on  "Telegraphic 
Communication,  especially  by  means  of  Galvanism."  This 
method  is  particularly  interesting  because  of  its  similarity 
to  the  Photophone,  invented  by  Alexander  Graham  Bell  and 
Sumner  Tainter  a  half  century  later.  Describing  his  idea 
Steinheil  says  in  part:  " Another  possible  method  of  bringing 
about  transient  movements  at  great  distances,  without  any 
intervening  conductor,  is  furnished  by  radiant  heat,  when 
directed  by  means  of  condensing  mirrors  upon  a  thermo- 
electric pile.*  A  galvanic  current  is  called  into  play,  which  in 
its  turn  is  employed  to  produce  declinations  of  a  magnetic 
needle.  The  difficulties  attending  the  construction  of  such 

*  In  recent  years  thermo-piles  have  been  developed  to  such  an  extent  that 
the  heat  radiated  by  stars  can  be  detected  and  measured.  W.  W.  Coblentz,  of 
the  U.  S.  Bureau  of  Standards,  has  described,  in  various  publications  issued  by 


10  RADIODYNAMICS 

an  instrument,  although  certainly  considerable,  are  not  in 
themselves  insuperable.  Such  a  telegraph  however  would 
only  have  this  advantage  over  those  semaphores  based  on 
optical  principles  —  namely,  that  it  does  not  require  the  con- 
stant attention  of  the  observer;  but,  like  the  optical  one,  it 
would  cease  to  act  during  cloudy  weather,  and  hence  partakes 
of  the  intrinsic  defects  of  all  semaphoric  methods."  * 

It  is  not  probable  that  Steinheil  ever  worked  this  idea  into 
usable  form,  as  no  accounts  of  experiments  can  be  found, 
but  to  him  is  the  credit  really  due  for  first  (1839)  suggesting 
a  means  of  signalling  without  conducting  wires  by  the  use  of 
radiant  energy,  and  his  was  in  all  probability  the  first  radio- 
telegraphic  system  disclosed  to  the  world. 

Another  way  of  conveying  intelligence  in  a  manner  closely 
related  to  those  already  given  depends  upon  the  sonorescent 
property  of  substances.  The  voice-controlled  transmitting 
beam  of  light  or  heat  is  allowed  to  fall  upon  suitable  material, 
such,  for  instance,  as  a  sheet  of  hard  rubber.  The  periodic 
expansion  and  contraction  of  this  material,  caused  by  the 
periodic  variations  in  the  intensity  of  the  heat  imparted  by 
the  beam,  cause  the  rubber  disc  to  reproduce  the  sounds  made 
near  the  transmitter. 

Davy's  Sound-relaying  System 

Edward  Davy,  in  1838,  proposed  a  system  of  wireless 
signalling,  which,  though  not  of  any  practical  value,  is  worthy 
of  mention  because  the  principle  involved  very  closely  re- 

that  institution,  micro-radiometers  which  are  sufficiently  sensitive  to  detect  the 
heat  of  a  standard  candle  at  fifty-three  miles.  Edison's  "  tasimeter,"  which 
he  devised  for  studying  the  streamers  of  the  sun  during  an  eclipse,  is  reported 
to  have  been  so  sensitive  that  a  person  at  a  distance  of  thirty  feet  could  produce 
a  perceptible  effect  merely  by  turning  his  face  toward  the  instrument.  The 
Crookes  radiometer,  the  Duddell  thermo-galvanometer,  and  the  bolometer 
bridge  may  also  be  used  as  detectors  of  radiant  heat. 
*  Sturgeon's  "Annals  of  Electricity,"  Mar.,  1839. 


WIRELESS  CONTROL  OF  MECHANISMS  II 

sembles  our  modern  schemes  of  relaying,  which  are  applied 
in  long-distance  telegraphy  and  kindred  branches  of  the  art. 
The  energy  is  transmitted  a  short  distance  to  a  receiver 
which  responds,  controls  a  local  source  of  energy,  and  sends 
the  signal  on  in  duplicate  to  the  next  station,  this  operation 
being  repeated  a  sufficient  number  of  times  to  bridge  the  re- 
quired distance.  Davy,  however,  had  in  mind  the  conjoint 
use  of  sound  and  electricity  for  accomplishing  this  end.  His 
plan  was  as  follows:  Stations  placed  about  a  mile  apart  should 
be  fitted  with  powerful  means  of  producing  sound  waves  to- 
gether with  suitable  means,  such  as  our  common  megaphones, 
for  directing  them  to  the  receiver  and  concentrating  them 
upon  some  delicate  form  of  vibratory  relay.  This  relay 
would  vibrate  in  resonance  with  the  transmitted  sound 
waves,  close  the  circuit  for  energizing  a  local  means  of  sound 
production  similar  to  the  first,  and  thus  relay  the  signals  on 
to  the  next  station.  Obviously,  such  a  system  was  impractical 
in  comparison  with  other  ideas  advanced  at  that  time, 
principally  because  of  the  numerous  stations  necessary  to 
bridge  a  relatively  short  distance,  and  the  power  required 
at  each  of  these  to  produce  sound  waves  of  sufficient  ampli- 
tude to  operate  the  vibratory  relay  a  mile  away.  John 
Gardner  of  England  has  developed  sensitive  vibratory  relays 
with  which  he  can  control  lights,  motors,  bells,  etc.,  across 
a  large  room  by  whistling  the  tone  corresponding  in  fre- 
quency to  the  natural  period  of  the  vibratory  diaphragm  or 
reed.* 

*  For  other  references  to  this  subject,  see  Signor  Senliq  d'  Andres,  Tele- 
graphic Journal,  vol.  ix,  p.  126;  A.  R.  Sennet,  Journ.  Inst.  Elec.  Eng.,  No.  137,  p. 
908.  See  also  U.  S.  Hydrographic  Office  Bulletin  of  May  13,  1914  on  the  "  Fes- 
senden  Oscillator  for  the  Detection  of  Icebergs,"  Professor  Dayton  C.  Miller's 
work  with  his '"  Phonodik,"  described  in  his  book  on  "The  Science  of  Musical 
Sounds  "  (Macmillan  Co.),  Tests  on  Fessenden  Submarine  Signalling  Apparatus, 
Journal  U.  S.  Art.  War,  Apr.  1915;  see  also  Sci.  Am.,  July  4,  1914 — and  the 
American  Magazine,  April,  1915. 


CHAPTER   III 
PRACTICAL  WIRELESS  TELEGRAPHY 

The  first  experiments  of  importance  with  the  new  earth 
conduction  telegraphy  appear  to  have  been  made  by  Professor 
Morse,  who,  in  1842,  actually  transmitted  signals  a  distance 
of  nearly  a  mile  across  the  Susquehanna  river.* 

In  a  letter  to  the  Secretary  of  the  Treasury  which  was  sub- 
sequently laid  before  the  House  of  Representatives,  Morse 
says:  .  , 

"In  the  autumn  of  1842,  at  the  request  of  the  American 
Institute,  I  undertook  to  give  to  the  public  in  New  York  a 
demonstration  of  my  telegraph,  by  connecting  Governor's 
Island  with  Castle  Garden,  a  distance  of  a- mile;  and  for  this 
purpose  I  laid  my  wires  properly  insulated  beneath  the 
water.  I  had  scarcely  begun  to  operate,  and  had  received 
but  two  or  three  characters  when  my  intentions  were  frus- 
trated by  the  accidental  destruction  of  a  part  of  my  con- 
ductors by  a  vessel,  which  drew  them  up  on  her  anchor,  and 
cut  them  off.  In  the  moments  of  mortification  I  immedi- 
ately devised  a  plan  for  avoiding  such  an  accident  in  the 
future,  by  so  arranging  the  wires  along  the  banks  of  the  river 
as  to  cause  the  water  itself  to  conduct  the  electricity  across. 
The  experiment,  however,  was  deferred  until  I  arrived  in 
Washington;  and  on  Dec.  16,  1842,  I  tested  my  arrangement 
across  the  canal  and  with  success.  The  simple  fact  was 
then  ascertained  -that  electricity  could  be  made  to  cross  a 
river  without  other  conductors  than  the  river  itself;  but  it 
was  not  until  the  last  autumn  that  I  had  the  leisure  to  make 

*  From  this  we  learn  that  Morse  actually  operated  a  wireless  telegraph 
before  his  Washington-Baltimore  wire  system  was  opened  for  service. 

12 


PRACTICAL   WIRELESS   TELEGRAPHY 


a  series  of  experiments  to  ascertain  the  law  of  its  passage. 
The  following  diagram  (Fig.  3)  will  serve  to  explain  the 
experiment : 

"A,  B,  C,  D  are  the  banks  of  the  river;  N,  P  is  the  battery; 
G  is  the  galvanometer;  ww  are  the  wires  along  the  banks 
connected  with  copper  plates,  f,  g,  h,  i,  which  are  placed  in 
the  water.  When  this  arrangement  is  complete,  the  elec- 
tricity, generated  by  the  battery,  passes  from  the  positive 
pole  P  to  the  plate  h,  across  the  river  through  the  water  to 

w ..d^r- 


plate  i,  and  thence  around  the  coil  of  the  galvanometer  to 
plate  f,  across  the  river  again  to  plate  g,  and  thence  to  the 
other  pole  of  the  battery.  The  distance  across  the  canal  is 
eighty  feet;  on  August  24  the  following  were  the  results  of 
the  experiment*  .  .  .  showing  that  electricity  crosses  the 
river  and  in  quantity  in  proportion  to  the  size  of  the  plates 
in  the  water.  The  distance  of  the  plates  on  the  same  side  of 
the  river  from  each  other  also  affect  the  result.  Having 
ascertained  the  general  fact  I  was  desirous  of  discovering  the 
best  practical  distance  at  which  to  place  my  copper  plates, 
and  not  having  the  leisure  myself,  I  requested  my  friend, 
Professor  Gale,  to  make  the  experiments  for  me."  .  .  . 

The  experiments  made  by  Professor  Gale  indicate  that  the 
distance  between  the  plates  along  the  shores  should  be  approxi- 
mately three  times  greater  than  that  from  shore  to  shore 

*  The  table  containing  information  only  of  general  interest  is  omitted. 


14  RADIODYNAMICS 

across  the  stream,  since  four  times  the  distance  did  not  give 
any  increase  in  power  and  less  than  three  times  the  distance 
diminished  the  deflections  of  the  galvanometer  considerably. 
Between  1854  and  1860  James  Bowman  Lindsay  made  similar 
attempts  at  wireless  telegraphy  by  utilizing  water  as  the 
conducting  medium. 

With  an  apparatus  like  that  of  Morse,  Lindsay  finally  suc- 
ceeded in  signalling  across  the  river  Tay,  where  it  is  more 
than  a  mile  wide.* 

J.  W.  Wilkins  of  the  Cooke  and  Wheatstone  Telegraph  Co. 
also  experimented  with  earth  conduction  telegraphy  in  1845, 
and  published  the  results  of  his  investigations  in  the  Mining 
Journal,  March  31,  1849,  under  the  heading  "  Telegraph 
Communication  between  England  and  France."  f 

Invention  of  the  Telephone 

After  the  invention  of  the  telephone,  in  1876,  wireless 
telegraphy  went  forward  with  leaps  and  bounds.  The 
marvelous  sensitiveness  of  this  instrument,  which  will  give 
audible  responses  under  the  application  of  less  than  one- 
millionth  of  a  volt  of  electromotive  force,  is  "largely  responsible 
for  the  great  progress  made  along  these  lines.  Even  wireless 
telephony  was  introduced. 

Its  use  in  a  telegraph  line  running  parallel  to  another  line 
through  which  telephone  conversation  and  singing  was  being 
carried,  led  to  the  accidental  discovery  of  its  extraordinary 
sensitiveness  to  induction  currents  in  1877,  by  Mr.  Charles 
Rathbone  of  Albany,  N.  Y.J 

*  See  "Electrical  Engineer,"  vol.  xxiii,  pp.  21-51;  Kerr,  "Wireless  Teleg- 
raphy," 1898,  p.  40. 

t  For  detailed  accounts  of  his  work  see  Fahie's  "History  of  Wireless 
Telegraphy,"  pp.  32-38. 

t  Journal  of  the  Telegraph,  Oct.  i  and  16;  and  Nov.  i,  1877.  For  simi- 
lar observations  see  Telegraphic  Journal,  Mar.  i,  1788,  p.  96;  Journal  of  the 
Telegraph,  Mar.  16,  1878,  Dec.  i,  1877;  The  Electrician,  vol.  vi,  pp.  207-303. 


PRACTICAL   WIRELESS   TELEGRAPHY  15 

These  observations  on  inductive  effects  in  telephone  cir- 
cuits began  to  be  investigated;  in  1877  Prof.  E.  Sacher  of 
Vienna  found  that  signals  from  three  Smee  cells  sent  through 
one  wire  120  m.  long  could  be  distinctly  heard  in  the  telephone 
in  another  and  parallel  wire  20  m.  distant.* 

Prof.  John  Trowbridge  of  Harvard  University  was  the  first 
to  systematically  study  the  problem  of  electromagnetic  in- 
duction signalling.  His  attention  is  concentrated  chiefly  on 
the  use  of  interrupted  or  alternating  currents  at  the  trans- 
mitter and  a  telephonic  receiver;  in  other  respects  his  circuit 
was  practically  the  same  as  Morse's  (Fig.  3).t 

In  1884  Trowbridge  described  another  plan  using  a  com- 
bination of  both  electromagnetic  induction  and  earth  con- 
duction; later  he  discussed  the  phenomena  of  induction, 
electromagnetic  and  electrostatic,  as  distinguished  from  leak- 
age or  earth  currents,  and  with  reference  to  their  employment 
in  wireless  telegraphy,  t 

Experiments  of  Alexander  Graham  Bell 

About  1882  Alexander  Graham  Bell  made  some  successful 
experiments  along  this  line  suggested  by  Trowbridge.  In  his 
paper  read  before  The  American  Association  for  the  Ad- 
vancement of  Science,  in  1884,  he  says: 

"A  few  years  ago  I  made  a  communication  on  the  use  of 
the  telephone  in  tracing  equipotential  lines  and  surfaces.  I 
will  briefly  give  the  chief  points  of  my  experiment,  which  was 
based  on  experiments  made  by  Professor  Adams  of  King's 
College,  London.  Professor  Adams  used  a  galvanometer  in- 
stead of  a  telephone. 

"In  a  vessel  of  water  I  placed  a  sheet  of  paper.     At  two 

*  Electrician,  vol.  i,  p.  194. 

t  His  investigations  are  discussed  in  detail  in  "The  Earth  as  a  Conductor 
of  Electricity,"  Am.  Acad.  Arts  and  Sc.,  1880;  see  also  "Silliman's  Am.  Journ. 
Sc.,  1880. 

J  Sc.  Am.  Supp.,  Feb.  21,  1891. 


16  RADIODYNAMICS 

points  on  that  paper  were  fastened  two  ordinary  sewing 
needles,  which  were  also  connected  with  an  interrupter  that 
interrupted  the  circuit  about  one  hundred  times  a  second. 

"Then  I  had  two  needles  connected  with  a  telephone;  one 
needle  I  fastened  on  the  paper  in  the  water,  and  the  moment 
I  placed  the  other  needle  in  the  water  I  heard  a  musical  sound 
in  the  telephone.  By  moving  this  needle  around  in  the 
water,  I  would  strike  a  place  where  there  would  be  no  sound 
heard.  This  would  be  where  the  electric  tension  was  the 
same  as  in  the  needle;  and  by  experimenting  in  the  water 
you  could  trace  out  with  perfect  ease  an  equipotential  line 
around  one  of  the  poles  in  the  water. 

"It  struck  me  afterwards  that  this  method,  which  is  true 
on  the  small,  is  also  true  on  the  large  scale,  and  that  it  might 
afford  a  solution  of  a  method  of  communicating  electric  signals 
between  vessels  at  sea. 

"I  made  some  preliminary  experiments  in  England,  and 
succeeded  in  sending  signals  across  the  river  Thames  in  this 
way.  On  one  side  were  two  metal  plates  placed  at  a  distance 
from  each  other,  and  on  the  other  two  terminals  connected 
with  the  telephone.  A  current  was  established  in  the  tele- 
phone each  time  a  current  was  established  through  the 
galvanic  circuit  on  the  opposite  side,  and  if  that  current  was 
rapidly  interrupted  you  would  get  a  musical  tone. 

"Urged  by  Professor  Trowbridge,  I  made  some  experiments 
which  are  of  very  great  value  and  suggestiveness.  The  first 
was  made  on  the  Potomac  river.  I  had  two  boats.  In  one 
boat  we  had  a  Leclanche  battery  of  six  elements,  and  an  in- 
terrupter for  interrupting  the  current  very  rapidly.  Over  the 
bow  of  the  boat  we  made  water  connection  by  a  metallic  plate, 
and  behind  the  boat  we  trailed  an  insulated  wire,  with  a 
float  at  the  end  carrying  a  metallic  plate,  so  as  to  bring  these 
two  elements  about  one  hundred  feet  apart.  I  then  took 
another  boat  and  sailed  off.  In  this  boat  we  had  the  same 


P&1CTICAL   WIRELESS   TELEGRAPHY  17 

arrangement,  but  with  a  telephone  in  the  circuit.  In  the 
first  boat,  which  was  moored,  I  kept  a  man  making  signals; 
and  when  my  boat  was  near  his  I  would  hear  those  signals 
very  well  —  a  musical  tone,  something  of  this  kind:  turn, 
turn,  turn.  I  then  rowed  my  boat  down  the  river,  and  at  a 
distance  of  a  mile  and  a  quarter,  which  was  the  farthest  I 
tried,  I  could  still  (distinguish  those  signals. 

"It  is  therefore  perfectly  practicable  fof  steam  vessels  with 
dynamo  machines  to  know  of  one  another's  presence  in  a  fog 
when  they  come,  say,  within  a  couple  of  miles  of  one  another, 
or,  perhaps  at  a  still  greater  distance.  I  tried  the  experiment 
a  short  time  ago  in  salt  water  of  about  twenty  fathoms  in 
depth;  I  used  then  two  sailing  boats,  and  did  not  get  so 
great  a  distance  as  on  the  Potomac.  The  distance,  which  we 
estimated  by  the  eye,  seemed  to  be  about  half  a  mile;  but 
on  the  Potomac  we  took  the  distance  accurately  on  the  shore.'7 

In  1886,  convinced  of  the  practicability  of  his  method,  Bell 
says  further: 

"Most  of  the  passenger  steamships  have  dynamo  engines 
and  are  electrically  lighted.  Suppose,  for  instance,  one  of 
them  should  trail  a  wire  a  mile  long,  or  any  length,  which  is 
connected  with  the  dynamo  engine  and  electrically  charged. 
The  wire  would  practically  have  a  ground  connection  by 
trailing  in  the  water.  Suppose  you  attach  a  telephone  to 
the  end  on  board.  Then  your  dynamo  or  telephone  end 
would  be  positive,  and  the  other  end  of  the  wire  trailing  be- 
hind would  be  negative.  All  of  the  water  about  the  ship 
will  be  positive  within  a  circle  whose  radius  is  one-half  the 
length  of  the  wire.  All  of  the  water  about  the  trailing  end 
will  be  negative  within  a  circle  whose  radius  is  the  other  half 
of  the  wire.  If  your  wire  is  one  mile  long  there  is  then  a 
large  area  of  water  about  the  ship  which  is  affected  either 
positively  or  negatively  by  the  dynamo  engine  and  -the 
electrically  charged  wire.  It  will  be  impossible  for  any  ship 


l8  RADIODYNAMICS 

or  object  to  approach  within  the  water  so  charged  in  relation 
to  your  ship  without  your  telephone  telling  the  whole  story 
to  the  listening  ear.  Now  if  a  ship  coming  in  this  area  has  a 
similar  apparatus,  the  two  vessels  can  communicate  with 
each  other  by  their  telephones.  If  they  are  enveloped  in 
fog,  they  can  keep  out  of  each  other's  way.  The  ship  having 
the  telephone  can  detect  other  ships  in  its  track,  and  keep 
out  of  the  way  in  a  fog  or  storm.  The  matter  is  so  simple 
that  I  hope  our  ocean  steamships  will  experiment  with  it.": 
This  method  of  signalling,  attempted  later  by  Messrs. 
Rathenau,  Rubens,  and  Strecker,  was  finally  carried  to  a 
distance  of  nearly  nine  miles,  but  the  advent  of  the  work  of 
Maxwell  and  Hertz  followed  by  the  practical  application  of 
their  theories  and  discoveries  by  Marconi  and  others,  proved 
such  an  advance  in  method,  and  the  futility  of  trying  to 
make  earth  conduction  systems  duplicate  the  records  of  the 
new  Hertzian-wave  telegraphy  was  so  evident  that  work  along 
that  line  was  practically  discontinued. 

*  Public  Opinion,  Jan.  31,  1886. 


CHAPTER  IV 


ELECTROSTATIC  AND  COMBINED  INDUCTION- 
CONDUCTION  TELEGRAPH  SYSTEMS 

Professor  Dolbear's  Electrostatic  Telegraph 

In  1882,  at  about  the  same  time  as  A.  G.  Bell,  Professor 
Dolbear  of  Tufts  College,  Boston,  was  also  engaged  on  the 
problem  of  wireless  telegraphy.  His  apparatus  was  some- 
what more  suggestive  than  any  hitherto  proposed  and  was 
awarded  a  United  States  patent  in  March,  1882.  The  fol- 
lowing is  an  extract  from  his  patent  specification: 

b 
Hi 


OR 


FIG.  4. 

"In  the  diagram  (Fig.  4),  A  represents  one  place  and  B 
a  distant  place.  C  is  a  wire  leading  into  the  ground  at  A, 
and  D  a  wire  leading  into  the  ground  at  B ;  G  is  an  induction 
coil  having  in  the  primary  circuit  a  microphone  transmit- 
ter, T,  and  a  battery,  F,  which  has  a  number  of  cells  suf- 
ficient to  establish  in  the  wire  C,  which  is  connected  with  one 
terminal  of  the  secondary  coil,  an  electromotive  force  of,  say, 

19 


20  RADIODYNAMICS 

ioo  volts.  The  battery  is  so  connected  that  it  not  only 
furnishes  the  current  for  the  primary  circuit,  but  also  charges 
or  electrifies  the  secondary  coil  and  its  terminals  C,  and  Hi. 

"Now  if  words  be  spoken  in  proximity  to  transmitter  T, 
the  vibration  of  its  diaphragm  will  disturb  the  electrical  con- 
dition of  the  coil  G,  and  thereby  vary  the  potential  of  the 
ground  at  B,  and  the  receiver  will  reproduce  the  words  spoken 
in  proximity  to  the  transmitter,  as  if  the  wires  CD  were  in 
contact,  or  connected  by  a  third  wire. 

"There  are  various  well-known  ways  of  electrifying  the 
wire  C  to  a  positive  potential  far  in  excess  of  ioo  volts,  and 
the  wire  D  to  a  negative  potential  far  in  excess  of  ioo  volts. 

"In  the  diagram,  H,  Hi,  Ha  represent  condensers,  the  con- 
denser Hi  being  properly  charged  to  give  the  desired  effect. 
The  condensers  H  and  H2  are  not  essential,  but  are  of  some 
benefit;  nor  is  the  condenser  Hi  essential  when  the  secondary 
coil  is  otherwise  charged.  I  prefer  to  charge  all  these  con- 
densers, as  it  is  of  prime  importance  to  keep  the  grounds  of 
wires  C  and  D  oppositely  electrified,  and  while,  as  is  obvious, 
this  may  be  done  by  either  the  batteries  or  the  condensers,  I 
prefer  to  use  both." 

In  the  Scientific  American  Supplement,  Dec.  n,  1886, 
Professor  Dolbear  gives  some  additional  particulars: 

"My  first  results  were  obtained  with  a  large  magneto 
electric  machine  with  one  terminal  grounded  through  a  Morse 
key,  the  other  terminal  out  in  free  air  and  only  a  foot  or  two 
long;  the  receiver  having  one  terminal  grounded,  the  other 
held  in  the  hand  while  the  body  was  insulated,  the  distance 
between  grounds  being  about  sixty  feet.  Afterward  -much 
louder  and  better  effects  were  obtained  by  using  an  induction 
coil  having  an  automatic  break  and  with  a  Morse  key  in  the 
primary  circuit,  one  terminal  of  the  secondary  grounded  the 
other  free  in  air,  or  in  a  condenser  of  considerable  capacity, 
the  latter  having  an  air  discharge  of  fine  points  at  its  opposite 


TELEGRAPH  SYSTEMS  21 

terminal.  At  times  I  have  employed  a  gilt  kite  carrying  a 
fine  wire  from  the  secondary  coil.  The  discharges  then  are 
apparently  nearly  as  strong  as  if  there  was  an  ordinary 
circuit. 

"The  idea  is  to  cause  a  series  of  electrical  discharges  into 
the  earth  without  discharging  into  the  earth  the  other  termi- 
nal of  the  battery  or  induction  coil  —  a  feat  which  I  have  been 
told  so  many  many  times  was  impossible,  but  which  certainly 
can  be  done.  An  induction  coil  isn't  amenable  to  Ohm's 
law  always!  Suppose  at  one  place  there  be  apparatus  for 
discharging  the  positive  pole  of  the  induction  coil  into  the 
ground,  say,  100  times  a  second,  then  the  ground  will  be 
raised  to  a  certain  potential  100  times  a  second.  At  another 
point  let  a  similar  apparatus  discharge  the  negative  pole  100 
times  a  second;  then  between  these  two  places  there  will  be 
a  greater  difference  of  potential  than  in  other  directions,  and 
a  series  of  earth  currents,  100  per  second,  will  flow  from  one 
to  the  other.  Any  sensitive  electrical  device,  a  galvanometer 
or  a  telephone,  will  be  disturbed  at  this  latter  station  by 
these  currents,  and  any  intermittence  of  them,  as  can  be 
brought  about  by  a  Morse  key  in  the  first  place,  will  be  seen 
or  heard  in  the  second  place.  The  stronger  the  discharges 
that  can  be  thus  produced,  the  stronger  will  the  earth  currents 
be  of  course,  and  an  insulated  tin  roof  is  an  excellent  terminal 
for  such  a  purpose.  I  have  generally  used  my  static  telephone 
in  my  experiments,  though  the  magneto  will  answer. 

"I  am  still  at  work  on  this  method  of  communication,  to 
perfect  it.  I  shall  soon  know  better  its  limits  on  both  land 
and  water  than  I  do  now.  It  is  adapted  to  telegraphing  be- 
tween vessels  at  sea. 

"Some  very  interesting  results  were  obtained  when  the 
static  receiver  with  one  terminal  was  used.  A  person  stand- 
ing on  the  ground  a  distance  from  the  discharging  point  could 
hear  nothing;  but  very  little  standing  on  ordinary  stones,  as 


22  RADIODYNAMICS 

granite  blocks  or  steps;  but  standing  on  asphalt  concrete,  the 
sounds  were  loud  enough  to  hear  with  the  telephone  at  some 
distance  from  the  ear.  By  grounding  one  terminal  of  the 
induction  coil  to  the  gas  or  water  pipes  and  leaving  the  other 
end  free,  telegraph  signals  can  be  heard  in  any  part  of  a  big 
building  and  its  neighborhood  without  any  connection  what- 
ever, provided  the  person  be  well  insulated." 

Explanation  of  Dolbear's  System 

Although  Professor  Dolbear's  circuit  arrangements  re- 
semble somewhat  those  of  Marconi,  his  system  lacked  the 
essential  features  which,  later,  were  applied  so  successfully, 
namely,  electrical  oscillations  of  high  frequency  at  the  trans- 
mitter and  suitable  detecting  apparatus  at  the  receiver. 

Dolbear's  results  were  clearly  those  of  electrostatic  induction 
and  not,  as  he  believed,  due  to  conducting  effects  through 
the  earth;  the  earth  connections  merely  served  to  furnish 
one  side  of  an  electrostatic  condenser,  the  other  sides  of 
which  were  supplied  by  the  elevated  conductors;  the  same 
results  can  be  secured  by  using  insulated  metallic  capacity 
areas,  now  known  as  counterpoises,  instead  of  the  earth  as 
the  lower  halves  of  the  radiating  and  receiving  aerial  systems. 
This  is  made  plain  by  a  study  of  the  drawings  taken  from  his 
patent  specification. 

The  functions  of  the  elevated  condensers,  H,  Hi,  and  H2, 
and  of  the  battery  b  (Fig.  4),  are  not  evident,  since  the  under- 
lying principle  upon  which  the  whole  system  is  based  does 
not  explain  their  necessity.  This  principle  is  nothing  more 
than  a  statement  of  the  laws  of  electrostatic  induction;  it 
can  best  be  understood  by  a  study  of  the  properties  and 
action  of  the  circuits  with  the  unnecessary  apparatus  omitted. 
At  the  transmitter  we  then  have  a  voice-controlled  source  of 
high  potential,  one  end  of  which  is  earthed  and  the  other  con- 
nected to  an  insulated  elevated  conductor.  At  the  receiver 


TELEGRAPH  SYSTEMS 


Stress  Lines  of 
Electrostatic  Field 


lew  fed  Charged 
Conductor 


we  have  a  similar  elevated  conductor  earthed  through  an 
electrostatic  telephone.  When  sound  waves  impinge  on  the 
microphone  of  the  transmitter,  fluctuating  currents  are  set 
up  in  the  primary  of  the  induction  coil;  these  produce  fluctu- 
ating potentials  at  the  terminals  of  the  secondary  winding, 
which  are  conducted  to  the  elevated  capacity  area;  the 
latter  with  the  earth  forms  an  electrostatic  condenser  with 
the  intervening  air  as  the  dielectric.  The  electrostatic  field 
of  force  of  this  condenser  extends  radially  out  and  down- 
wards from  the  aerial  wire 
in  curved  lines,  as  is  graphi- 
cally shown  in  the  accom- 
panying diagram.  (Fig.  5.) 
Now  .if  an  insulated  body, 
such  as  the  elevated  wire 

i-    ,-i  •  T  '.,1   •  -•'••-•i~''  -'  ••<-.:-  .•  -Earth*  '"'  " 

of  the  receiver,  lies  within 

this  field  of  force,  potentials  FlG>  5> 

will  be  induced  on  it,  the  amplitude  of  which  varies  in  unison 

with  the  variations  of  potential  on  the  transmitting  aerial 

wire. 

Since  the  earthed  plate  of  the  electrostatic  telephone  in 
the  receiver  remains  constant  at  the  earth's  potential  and 
since  the  other  plate  is  connected  to  the  elevated  wire  and 
subject  to  the  inductive  action  of  the  transmitter,  a  varying 
difference  of  potential  is  therefore  set  up  between  the  plates, 
with  a  consequent  variation  of  attraction  between  them. 
One  of  the  plates,  which  is  a  diaphragm  of  flexible  metal  or 
of  some  such  material  as  thin  sheet  mica  covered  with  a  tin 
foil  conducting  area,  is  therefore  made  to  vibrate  and  repro- 
duce sounds  produced  at  the  transmitter. 

Lowenstein's  Electrostatic  Telegraph 

Mr.  Fritz  Lowenstein,  a  consulting  and  research  engineer 
of  New  York,  engaged  in  radio  research  work,  suggested  a 


24  RADIODYNAMICS 

similar  method'  of  signalling  to  short  distances  in  iqi2. 
This  was  based  principally  upon  the  marvellous  sensitiveness 
of  his  potential  operated  receiving  device.  It  could  be  used 
advantageously  with  the  (magneto)  telephone  and  was 
therefore  adapted  for  both  telegraphy  and  telephony;  the 
telegraphic  system,  however,  gave  the  best  results  for  dis- 
tance; telegraphic  signals  were  sent,  with  his  apparatus,  from 
his  laboratory  at  115  Nassau  Street  to  the  Liberty  Build- 
ing at  the  corner  of  Nassau  and  Liberty  streets,  about  a 
half  mile  distant.  The  transmitter  consisted  of  a  2o,ooo-volt 
transformer,  the  primary  of  which  was  energized  by  a  500- 
cycle  alternating  current.  One  terminal  of  the  secondary 
was  grounded  to  the  water  pipe  system;  the  other  was  con- 
nected to  a  single,  nearly  vertical  conductor  (No.  8  stranded 
copper),  the  upper  well-insulated  end  of  which  extended  to  a 
drop  wire  from  the  top  of  a  three  hundred-foot  office  building 
nearby. 

The  receiving  station  near  the  top  of  the  Liberty  Building 
consisted  of  a  one  hundred-foot  length  of  bell  wire  suspended 
from  a  pole  out  one  of  the  windows  and  connected  to  Mr. 
Lowenstein's  ion  controller  detector,*  the  other  terminal  of 
which  was  grounded  to  the  water  pipes.  The  sensitive 
telephone  connected  to  the  instrument  clearly  indicated  the 
Morse  signals  sent  out  at  the  transmitter.-  These  were  made 
by  opening  and  closing  the  primary  circuit  of  the  transformer 
with  a  Morse  key. 

Passing  over  the  work  of  Thomas  A.  Edison,  W.  F.  Melruish, 
C.  A.  Stevenson,  Professor  Erich  Rathenau,  and  others,  we 
come  to  another  serious  attack  on  the  problem  of  wireless  teleg- 
raphy, which  was  executed  in  a  masterly  way  by  Sir  William 
Preece,  engineer-in-chief  of  the  postal  telegraph  system  in 
England. 

*  A  potential-operated,  ionized  gas-detector  and  amplifier  for  radio- 
telegraphy,  radiotelephony,  and  wire  telephony. 


TELEGRAPH  SYSTEMS 


Preece's  Induction-Conduction  System 

Preece's  system  was  a  combination  of  three  previously 
existing  systems,  namely,  earth  conduction,  electrostatic 
induction,  and  electromagnetic  induction.  Although  it  is 
certain  that  each  of  these  three  phenomena  played  a  part  in 
the  transmission  of  the  signals,  their  relative  importance  has 
not  been  definitely  determined.  A  brief  explanation  will 
serve  to  make  his  method  clear. 

The  signals  were  transmitted  between  two  long,  horizontal 
wires,  one  at  the  transmitter  and  one  at  the  receiver.  These 


Condenser 


Listening-//!  tfey 


'Earth 


Receiving  Telephone 


FIG.  6. 


Earth 


wires  were  supported  parallel  to  one  another  on  telegraph 
poles  and  were  connected  to  earth  plates  of  considerable  area 
at  their  two  ends.  The  diagram,  Fig.  6,  shows  the  con- 
nections at  each  station,  which  is  a  combined  transmitter  and 
receiver.* 

The  pulsating  currents  through  the  sending  wire  and  the 
earth  produce  a  variable  electromagnetic  and  electrostatic 
field,  which  induces  a  fluctuating  E.M.F.  in  the  receiving  cir- 
cuit. This  is  indicated  by  sounds  in  the  telephone.  The  in- 
duced currents  are  also  augmented  by  the  currents  conducted 
through  the  earth  itself. 

*  The  use  of  a  "  breaking-in "  key  in  this  circuit  will  be  found  very  inter- 
esting to  practical  operators  since  a  number  of  inventors,  within  the  last  few 
years,  have  brought  forward  this  principle  as  novel  for  use  in  radio  systems. 


26  RADIODYNAMICS 

It  has  been  shown  that  the  hemispheroidal  mass,  repre- 
sented by  the  lines  of  current-flow  from  one  plate  to  the  other, 
can  be  replaced  electrically  by  a  resultant  conductor  of  defi- 
nite form  and  position.  This  is  illustrated  in  Fig.  7,  where 
L  is  the  line  wire,  PP  the  earthed  plates,  POP,  PAP,  etc., 
the  equipotential  lines  of  current-flow,  and  R  the  resultant 
conductor.  The  induction  effects  occurring  between  two  such 
circuits  are  therefore  the  same  as  if  they  were  composed 
entirely  of  metallic  conductors  of  the  same  physical  and 
electrical  characteristics  as  the  line  wires  with  their  result- 
ant earth  conductors.  At  Loch  Ness,  where  the  parallel 
wires  were  about  three  miles  long,  the  calculated  depth  of  the 

L 


resultant  earth  conductor  was  about  nine  hundred  feet.  This 
arrangement  of  parallel  line  wires  with  earthed  ends  therefore 
gave  all  the  advantages  of  signalling  between  huge,  single-turn 
coils,  with  the  increased  effect  due  to  earth  conduction,  and 
without  the  almost  insuperable  difficulties  involved  in  con- 
structing such  coils  above  the  earth. 

In  March,  1898,  this  system  was  permanently  established 
for  signalling  between  Lavernock  Point,  on  the  mainland, 
and  Flat-Holm  in  the  Bristol  Channel,  a  distance  of  over 
three  miles.  Fifty  Leclanche  cells  and  an  interrupter  fre- 
quency of  four  hundred  makes  and  breaks  per  second  were 
used  for  transmitting,  and  a  telephone  served  as  the  receiving 
indicator.  The  signals  were  very  distinct,  and  it  is  said  a  speed 
of  forty  words  a  minute  has  been  attained  without  difficulty. 


CHAPTER  V 
ELECTROMAGNETIC  WAVE  SYSTEMS 

The  profound  speculations  and  mathematical  researches  of 
Maxwell  on  the  electromagnetic  nature  of  light,  followed  by 
the  brilliant  work  of  Hertz  and  his  successors,  are  so  familiar 
to  the  scientific  public  that  a  brief  resume  of  the  evolution  of 
the  art  is  here  sufficient. 

Again  we  see  that  radio  signalling,  like  most  wonders  of 
science,  has  not  been  an  invention,  in  the  popularly  accepted 
meaning  of  the  word,  but  rather  a  gradual,  step-by-step  de- 
velopment in  which  many  prominent  men  of  science  have 


M 

FIG.  8. 
m  EE  is  the  glass  tube.  P,  P,  the  connectors,  and  M,  the  filings. 

played  a  part.  Maxwell's  theories,  published  in  1865,  laid 
the  foundation,  and  Hertz,  by  a  long  and  carefully  executed 
series  of  experiments,  paved  the  way;  Hertz's  successors, 
men  who  foresaw  the  practical  value  of  these  discoveries, 
utilized  the  material  he  laid  bare  for  the  production  of  a 
serviceable  means  of  communication. 

The  greatest  need  in  the  extension  of  Hertz's  work  to 
greater  distances,  was  a  receiving  wave  detector  of  high 
sensitiveness.  A  crude  form  of  such  a  detector  had,  as  early 
as  1866  been  used  by  S.  A.  Varley  as  a  lightning  arrester. 
In  1890  Prof.  E.  Branly  of  the  Catholic  University  of  Paris 
rediscovered  the  effects,  already  utilized  by  Varley,  of  Hertzian 

27    • 


28 


RADIODYNAMTCS 


waves  on  the  conductivity  of  metallic  filings.  He  also  ob- 
served the  restoring  or  decohering  effect  of  light  tapping  on 
the  filings  tube.  In  1893  Sir  Oliver  Lodge  repeated  Hertz's 
experiments,  using  the  "Branly  tube,"  or  "  coherer,"  as  he 


Capacity  Ana 


FIG.  9. 

called  it,  in  place  of  the  micrometer  spark  gap  in  the  Hertz 
resonator.  Branly 's  coherer  is  shown  in  Fig.  8.  Lodge's 
apparatus,  connected  for  reception  of  signals,  is  shown  dia- 
grammatically  in  Fig.  9.  With  this  apparatus  he  was  able  to 
observe  Hertzian  waves  at  distances  up  to  about  150  feet. 

Early  Work  of  Nikola  Tesla 

Nikola  Tesla,  after  completing  the  application  of  his  dis- 
covery of  the  rotating  magnetic  field  to  electric  motors  in 
1888,  turned  his  attention  to  the  problem  of  transmitting 
electrical  energy  to  a  distance  without  wires.  His  earliest 
plans  were  to  transmit  energy  not  only  in  small  amounts,  for 
purposes  of  communication,  but  also  in  amounts  sufficient  for 
industrial  purposes. 

The  first  public  announcements  of  these  plans  were  made  in 
February  and  March,  1893.  He  delivered  lectures  before  the 
Franklin  Institute  in  Philadelphia,  and  the  National  Electric 
Light  Association  in  St.  Louis.  However,  in  1891,  he  had 
already  described  and  shown,  in  a  lecture  before  a  scientific 
society,  a  method  of  lighting  an  electric  lamp  at  a  short  dis- 
tance without  connecting  wires.  High-frequency  oscillations 
were  used  in  these  experiments,  but  the  power  of  the  apparatus 
was  small  in  comparison  with  that  of  his  later  lectures  and 
experiments. 


ELECTROMAGNETIC  WAVE  SYSTEMS  29 

In  these  lectures  he  expressed  the  conviction  that:  "It 
certainly  is  possible  to  produce  some  electrical  disturbance 
sufficiently  powerful  to  be  perceptible  by  suitable  instruments 
at  any  point  on  the  earth's  surface." 

Describing  his  plan  in  detail  he  says: 

"Assume  that  a  source  of  alternating  currents  be  connected 
as  shown  in  the  accompanying  diagram  (Fig.  10)  with  one  of  its 
terminals  connected  to  earth  (convenient  to  the  water  mains) 
and  with  the  other  to  a  body  of  large  surface,  P.  When  the 
electric  oscillation  is  set  up,  there  will  be  a  movement  of  electri- 
city in  and  out  of  P,  and  alternating  currents  will  pass  through 
the  earth,  converging  to  or  diverging  from  the  point  C,  where 


FIG.  10. 

the  ground  connection  is  made.  In  this  manner  neighboring 
points  on  the  earth's  surface  within  a  certain  radius  will  be 
disturbed.  But  the  disturbance  will  diminish  with  the  dis- 
tance, and  the  distance  at  which  this  effect  will  still  be  per- 
ceptible will  depend  on  the  quantity  of  electricity  set  in  motion. 
Since  the  body  P  is  insulated,  in  order  to  displace  a  considerable 
quantity  the  potential  of  the  source  must  be  excessive,  since 
there  would  be  limitations  as  to  the  surface  of  P.  The  condi- 
tions might  be  adjusted  so  that  the  generator  or  source,  S,  will 
set  up  the  same  electrical  movement  as  though  its  circuit  were 
closed.  Thus  it  is  certainly  practicable  to  impress  an  electric 
vibration,  at  least  of  a  certain  low  period,  upon  the  earth. 
Theoretically  it  should  not  require  a  great  amount  of  energy 
to  produce  a  disturbance  perceptible  at  great  distance,  or  even 


30  RADIODYNAMICS 

all  over  the  surface  of  the  globe.  Now,  it  is  quite  certain  that 
at  any  point  within  a  certain  radius  of  the  source,  S,  a  properly 
adjusted  self-induction  and  capacity  device  can  be  set  in  action 
by  resonance.  Not  only  can  this  be  done,  but  another  source 
Si,  similar  to  S  or  any  number  of  such  sources,  may  be  set  to 
work  in  synchronism  with  the  latter,  and  the  vibration  thus 
intensified  and  spread  over  a  large  area;  or  a  flow  of  electricity 
produced  to  or  from  the  source  Si,  if  the  same  be  of  opposite 
phase  to  the  source  S.  Proper  apparatus  must  first  be  pro- 
duced, by  means  of  which  the  problem  can  be  attacked,  and  I 
have  devoted  much  thought  to  this  subject." 

Tesla  continued  his  investigations  along  these  lines  and  in 
1898  had  already  developed  apparatus  of  great  power  giving  a 
pressure  of  four  million  volts  and  discharges  extending  through 
sixteen  feet.  At  that  time  and  even  today  this  is  considered 
remarkable.  From  1899  to  I9°°  ne  continued  his  investiga- 
tions and  in  1900  he  published,  in  the  Century  Magazine,  a 
long  article  of  absorbing  interest  and  of  great  suggestiveness  on 
"The  Problem  of  Increasing  Human  Energy."  Therein  he 
described  and  illustrated  with  actual  photographs  his  appara- 
tus for  producing  pressures  of  over  twelve  million  volts  and 
capable  of  delivering  energy  at  the  rate  of  seventy-five  thou- 
sand horse-power. 

Professor  PopofFs  Receiver 

Professor  Popoff,  in  a  communication  to  the  Physico- 
Chemical  Society  of  St.  Petersburg,  in  1895,  described  a 
form  of  receiving  apparatus  designed  by  him  for  the  study 
of  atmospheric  electricity.  His  circuit  arrangement  which  is 
shown  in  Fig.  n  is  different  from  that  of  Lodge  in  that  one 
terminal  of  the  coherer  is  grounded,  and  the  other  is  connected 
to  a  vertical  conductor  extending  above  the  housetop.  Here 
is  introduced  the  well-known  method  of  utilizing  the  electric 
signal  bell  for  an  automatic  decoherer.  Professor  Popoff  also 


ELECTROMAGNETIC  WAVE  SYSTEMS  31 

used  a  form  of  tape  recorder  which  automatically  recorded 
the  duration  of  the  electrical  disturbances  in  the  atmosphere. 
This  apparatus  and  circuit  arrangement  is  precisely  the  same 
as  that  used  by  Marconi  in  his  early  experiments.  That 
Popoff  foresaw  the  possibilities  of  his  receiver  for  Hertzian 
wave  telegraphy  is  clearly  evidenced  by  the  concluding  para- 


FIG.  ii. 

graph  of  a  paper  read  before  the  Institute  of  Forestry  of 
St.  Petersburg.  "In  conclusion,"  he  says,  "I  may  express 
the  hope  that  my  apparatus,  with  further  improvements, 
may  be  adapted  to  the  transmission  of  signals  to  a  distance 
by  the  aid  of  quick  electric  vibrations  (high-frequency  oscilla- 
tions) as  soon  as  a  means  of  producing  such  vibrations  possess- 
ing sufficient  energy  is  found." 

Marconi's  Early  Work 

With  Hertz's  oscillator  and  PopofFs  receiver  Marconi  began 
his  experiments  on  his  father's  estate  near  Bologna,  Italy,  in 
1895.  Although  only  22  years  of  age  he  had  already  acquired 
much  knowledge  of  Hertzian  waves,  having  studied  under 


32  RADIODYNAMICS 

Professor  Rosa  of  the  Leghorn  Technical  School,  and  ac- 
quainted himself  with  the  published  writings  of  Professor 
Righi  of  the  University  of  Bologna.  After  a  year  of  experi- 
menting Signor  Marconi  went  to  England  and  filed,  in  the 
Patent  Office  of  Great  Britain,  an  application  for  a  patent, 
which  was  duly  granted. 

Later  Improvements 

Improvements  in  both  the  more  efficient  generation  and 
reception  of  the  electromagnetic  waves  have,  since  1895, 
chiefly  engaged  the  attention  of  radio  investigators.  Among 
the  more  important  advances  may  be  mentioned  the  intro- 
duction of  the  Tesla  high-frequency  transformer  for  coupled 
circuits  by  Lodge  and  Braun,  instead  of  the  direct  spark- 
excited  antenna  of  Marconi;  the  discovery  and  adoption  of 
detectors  suitable  for  use  with  the  telephone ;  the  introduction 
of  alternating  current  and  high  spark  frequencies  for  trans- 
mission; the  utilization  of  Wien's  discovery  of  the  quenched 
spark  gap;  and  the  more  recent  attacks  on  the  problem  of 
selectivity.  The  recent  work  of  Fessenden,  Alexanderson, 
and  Goldschmidt  on  the  direct  production  of  high-frequency 
alternating  current  of  continuous  amplitude  for  electric  wave 
telegraphy  and  telephony,  is  worthy  of  mention. 


CHAPTER  VI 


POSSIBLE  CONTROL   METHODS   FOR  RADIO- 
DYNAMICS  —  SOUND  WAVES 

Every  teledynamic  system  has  two  principal  parts,  namely, 
(i)  the  apparatus  for  the  transmission  and  reception  of  the 
controlling  energy,  and  (2)  the  apparatus  or  mechanisms  to 
be  controlled.  This  broad  subdivision  applies  to  such  simple 
forms  as  the  telegraph,  where  the  energy-transmitting  medium 
is  a  metallic  conductor,  and  the  receiver  a  relay  controlling 
a  sound-producing  mechanism,  as  well  as  to  the  very  com- 
plicated systems  utilizing  the  ether  as  the  connecting  link. 

Of  these  two  divisions  the  first  is  to  us  by  far  the  most 
important,  if  for  no  other  reason  because  of  the  difficulty  it  has 
presented  in  the  practical  solution  of  such  representative 
problems  as  torpedo  control.  It  therefore  demands  careful 
consideration,  especially  with  reference  to  a  proper  selection 
of  the  kind  of  radiant  or  other  energy  to  be  used. 

The  following  table  gives  some  of  the  most  important  forms 
of  radiant  energy  in  ether  and  air,  their  vibration  frequencies, 
and  detecting  means  capable  of  actuating  mechanisms: 


Waves 

Frequency  per  sec. 

Detector 

Acoustic  

1  6         to  35,000 

Vibratory  relay 

Hertzian  

50,000  to  2     billions 

Hertzian  wave  detector 

Infra-red,  or  heat  
Visible 

2               tO  40OO        " 

4000     to  8000      '  ' 

Thermoelectric  cells 
Selenium  cells 

Ultra-violet  

8000     to     ? 

Trigger  vacuum  tube. 

Besides  these  radiant  energy  means  we  may  mention 
earth  conduction,  electrostatic  induction,  and  electromag- 
netic induction. 

33 


34  RADIODYNAMICS 

Choice  of  Control  Energy 

A  number  of  important  factors  must  be  taken  into  con- 
sideration in  order  to  make  the  best  choice  of  these  several 
control  methods.  Although  the  Hertzian  wave  system  is 
employed  in  nearly  all  of  the  suggested  applications  of  radio- 
dynamics,  and  is  to  all  appearances  the  most  reliable  and 
best,  who  can  say  that  any  one  of  these  other  possible  methods, 
if  it  received  the  proper  attention,  would  not  be  much  simpler, 
and  at  the  same  time  still  more  reliable? 

Reliability  is  the  factor  of  prime  importance  in  the  abso- 
lute and  accurate  control  of  a  dangerous  weapon  like  a  torpedo, 
travelling,  as  it  does,  at  a  speed  of  between  thirty  and  forty 
miles  per  hour  and  carrying  large  quantities  of  highly  ex- 
plosive material.  Simplicity,  freedom  from  accidental  or 
intentional  interference,  and  cost  are  other  points  which 
demand  careful  thought.  The  maximum  range  at  which 
control  is  necessary,  and  indeed  possible,  is  limited  by  vision. 
This,  in  clear  weather,  does  not  exceed  eight  miles,  for  even 
with  a  good  binocular  the  torpedo  cannot  be  seen  beyond 
that  distance.  In  cloudy  or  stormy  weather  the  operations 
may  be  limited  to  two  or  three  miles.  This  does  not  mean 
that  the  usefulness  of  the  wirelessly  directed  torpedo  is 
limited  to  calm,  clear  weather,  for  any  attacking  fleet  or  ship 
would  be  subject  to  the  same  conditions,  inasmuch  as  the 
distance  and  accuracy  of  their  fire  is  greatly  affected  by  the 
condition  of  the  sea  and  weather. 

Difficulties  to  be  Overcome 

The  reader  may  think  of  the  four-thousand  mile  accom- 
plishments of  modern  radiotelegraphy  and  immediately  con- 
clude that  the  problem  of  getting  a  sufficient  amount  of 
energy  to  the  vessel  is  one  of  comparative  simplicity.  On 
the  contrary  this  is  one  of  the  chief  difficulties,  and  it  has  only 
lately  begun  to  be  surmounted. 


SOUND  WAVES  35 

The  following  table  will  serve  in  a  rough  way  to  show  the 
comparison  between  transmitted  and  received  energies  in 
various  types  of  electrical  energy- transmitting  systems: 

Watts  transmitted  Watts  received  Ratio 

Power  line io6               io6  i 

Cable  telegraph i                  icf"3  lo"3 

Telephone icr2            icr6  icr4 

Radiotelegraphy io5               icr8  icr13 

From  this  table  it  may  be  seen  that  of  the  one  hundred  kilo- 
watts used  at  a  high-power  radiotelegraphic  transmitting 
station  but  one  ten- trillion th  part  is  received  at  a  distance 
corresponding  to  the  maximum  working  range,  i.e.,  the 
range  at  which  the  received  power  is  measured  in  hundred- 
million  ths  of  a  watt.  This  range  in  daylight  is  usually  in  the 
neighborhood  of  three  thousand  miles,  but  is  subject  to  con- 
siderable variation  from  day  to  day  and  from  season  to  season; 
the  night  range  is  also  very  much  greater  than  the  day  range 
during  those  parts  of  the  year  when  atmospheric  disturbances 
cause  the  least  amount  of  interference. 

In  long-distance  radiotelegraphic  sets  the  transmitter  is  of 
such  power  (25  to  100  kw.),  as  would  be  excessive  for  torpedo 
control  in  coast  defence.  But  far  more  important  than  this 
is  the  fact  that  the  telephone,  which  is  used  as  the  receiving 
indicator  in  wireless  telegraph  sets,  will  give  readable  signals 
under  an  impressed  e.m.f.,  of  less  than  one-millionth  of  a  volt, 
while  to  trip  the  most  sensitive  relay  under  ideal  conditions 
requires  about  one-thousandth  of  a  volt  e.m.f.  applied  to 
its  terminals.  Under  the  conditions  of  shock  and  vibration 
aboard  a  small  vessel  in  a  rough  sea  the  restoring  spring  of 
such  an  instrument  must  be  set  under  sufficient  tension  to 
prevent  the  making  of  false  contacts;  the  sensitiveness  is 
thereby  reduced  to  from  one-fifth  to  one-tenth  of  its  highest 
value.  From  these  values  we  can  readily  see  that  a  radio- 
telegraphic  receiver  may  easily  be  as  much  as  5000  times  as 


RADIODYNAMICS 


sensitive  as  the  type  necessary  for  the  absolutely  reliable 
control  of  mechanisms.  Practically  all  systems  of  wireless 
signalling  depend  for  their  long-distance  operation  on  this 


FIG.  12. 

Prof.  Fesseriden's  submarine  sound  signalling  apparatus  used  to  detect  the 
presence  of  submarines.     (Published  by  permission.) 

extraordinary  sensibility  of  the  telephone;  when  used  with  a 
relay  the  distance  over  which  they  are  operative  likewise  de- 
creases tremendously. 

Sound  Waves  in  Radiodynamics 

The  employment  of  sound  waves  in  air  for  radiodynamics  has 
not  been  productive  of  any  noteworthy  results.     Submarine 


SOUND  WAVES  37 

signalling,  however,  has  been  developed  to  the  point  where 
the  transmitting  bell  signals  have  been  received  at  distances 


FIG.  13. 
Operator  sending  submarine  sound  signals  with  the  Fessenden  apparatus. 

(Courtesy  of  the  American  Magazine.) 

up  to  about  25  miles.     Prof.  R.  A.  Fessenden,  one  of  the 
pioneers  and  authorities  on  radiotelegraphy  in  the  United 


38  RADIODYNAMICS 

States,  signalled  across  Massachusetts  Bay  during  the  spring 
of  1914,  with  a  submarine  sound  wave  apparatus  which  he 
invented.  Figs.  12,  13,  14  and  15  show  Professor  Fessenden 
and  various  parts  of  his  submarine  signalling  system.  These 


FIG.  14. 

Vibrating  steel  diaphragm  used  as  both  transmitter  and  receiver  in  the  Fessen- 
den submarine  signalling  system.     (Courtesy  of  the  American  Magazine.} 

photographs  are  reproduced  through  the  courtesy  of  the 
American  Magazine.* 

Although  little  has  been  done  with  this  signalling  system 
in  adapting  it  to  the  severe  requirements  of  torpedo  control, 
its  possibilities  are  not  unworthy  of  consideration. 

The  fact  that  most  steamships,  war  vessels,  and  submarine 
boats  are  now  equipped  with  submarine  signalling  apparatus 
is  ample  proof  of  the  practicability  of  this  system  for  fog  and 

*  For  further  details  of  submarine  signalling  apparatus  see:  Jour.  Am. 
Soc.  Nav.  Engrs.,  Aug.,  1914;  Mar.  Engr.  and  Nav.  Archt.,  May,  1914;  Proc. 
Am.  Inst.  Elec.  Engrs.,  July,  1912. 


SOUND  WAVES 


39 


warning  signalling.  As  practiced,  a  submerged  bell,  electri- 
cally operated,  is  used  as  the  transmitter,  while  a  submerged 
microphone  transforms  the  received  sound  waves  into  elec- 
trical effects  observable  upon  a  telephone  receiver;  this  re- 
ceiving apparatus  is  in  all  respects  the  same  in  principle  as 
the  ordinary  telephone  which  we  have  in  our  offices  and 


FIG,  15. 

Professor  Reginald  A.  Fessenden  taking  observations  on  the  sound  waves  sent 
out  by  submarines.     (Courtesy  of  the  American  Magazine.) 

homes.  An  electric  ear  of  this  kind  is  usually  installed  on 
each  side  of  the  vessel,  and  two  telephones  provided  in  the 
pilot  house  for  the  observer.  By  switching  from  one  to  the 
other  of  these  the  general  direction  of  the  transmitter  can 
usually  be  determined,  since  the  receiving  microphone  on  the 
side  of  the  boat  nearest  the  bell  will  give  the  stronger  signal. 
When  the  signals  are  of  equal  strength  in  both  telephones  the 
direction  of  the  bell  at  the  dangerous  reef  can  be  determined 


40  RADIODYNAMICS 

by  swinging  the  ship.  The  practicability  of  apparatus  based 
on  such  an  energy  transfer  method  although  not  assured  is 
not  wholly  uncertain.  One  advantage  of  no  mean  impor- 
tance is  that  the  torpedo  could  be  entirely  submerged,  offering 
no  target  for  the  enemy's  gun  fire.  Every  other  system  ex- 
cept earth  conduction  in  practice  would  require  a  portion  of 
the  receiving  apparatus  to  project  above  the  water. 

By  utilizing  sound  waves  of  frequencies  below  the  audible 
limit  (16  per  second),  the  control  impulses  could  not  be 
detected  by  the  enemy  unless  they  were  provided  with  special 
apparatus  for  that  purpose.  If  such  a  transmitter  be  used 
with  tuned  mechanical  elements  in  connection  with  current 
amplifying  devices  at  the  receiver,  it  is  possible  that  an 
extremely  simple  and  effective  system  of  control  could  be 
developed.*  The  torpedo,  although  invisible,  could  be  ac- 
curately located  by  means  of  two  submerged  microphones, 
which  would  respond  to  signals  sent  out  by  the  torpedo 
itself.  This  scheme  has  been  used  in  the  European  War 
to  detect  the  presence  of  hostile  submarine  boats.  The 
principal  difficulties  to  be  met  in  the  use  of  submarine 
sound  waves  for  torpedo  control  are  the  interfering  signals, 
which  the  enemy  might  easily  send  out,  and  the  very  weak 
electrical  effects  produced  by  the  transmitter  at  battle-range 
distances.  The  former  is  an  extremely  difficult  problem. 
The  latter  might  be  overcome  by  using  a  simple  form  of 
amplifier,  such  as  De  Forest's. 

*  Such  a  scheme  was  described  by  the  author  in  a  lecture  on  The  Wirelessly 
Directed  Torpedo,  before  the  Indianapolis-Lafayette  section  of  the  American 
Institute  of  Electrical  Engineers  in  October,  1913. 


CHAPTER  VII 
INFRA-RED  OR  HEAT  WAVES 

Omitting  Hertzian  waves  for  the  present  we  come  to  the 
infra-red  rays  as  a  possible  means  of  effecting  mechanism 
operation  at  a  distance.  The  great  sensitiveness  of  the 
bolometer,  thermo-pile,  and  other  thermal  and  thermo- 
electric detectors  suggests  the  use  of  these  rays  as  a  form  of 
wave  energy  capable  of  serving  our  needs. 

No  mention  of  the  use  of  radiant  heat  for  operating  dis- 
tant switches  has  been  found  in  scientific  literature.  As  a 
means  of  telephoning  to  short  distances,  however,  it  was 
among  the  first  to  be  suggested,  as  previously  stated. 

Stimulated  by  the  accounts  of  the  extreme  sensitivity  of 
radiant  heat  detectors  and  of  their  use  in  the  measurement  of 
stellar  radiations,  the  writer  has  given  some  thought  to  the 
possibility  of  using  heat  waves  as  a  control  agency  in  a  system 
for  the  wireless  direction  of  torpedoes. 

Let  us  consider  first  the  general  advantages  and  disadvan- 
tages of  such  a  control  energy,  assuming  that  we  have  generat- 
ing means  of  such  power  and  receiving  detectors  of  such 
sensitiveness  that  we  are  able  to  control  switches  at  useful 
distances. 

One  of  the  first  advantages,  and  perhaps  the  greatest,  lies 
in  our  ability  to  direct  this  energy  at  will.  By  means  of  the 
highly-polished,  parabolic  surfaces  of  such  metals  as  silver 
and  zinc,  we  can  direct  practically  the  whole  of  our  generated 
energy  into  a  beam  of  parallel  rays.  Surfaces  of  silver  and 
zinc,  when  well  polished,  will  absorb  no  more  than  two  or  three 

41 


42  RADIODYNAMICS 

per  cent  of  the  incident  radiant  energy,  the  remaining  ninety- 
eight  or  ninety-seven  per  cent  being  reflected. 

In  order  to  secure  the  advantages  of  direction  by  the  use  of 
parabolic  reflectors,  we  must  confine  our  source  of  heat  to  a 
comparatively  small  area.  But  if  the  area  be  small  the  rate 
at  which  the  energy  is  radiated  per  unit  of  area  must  be 
correspondingly  large.  A  high  radiation  rate  per  unit  of  area 
can  only  be  obtained  with  a  high  temperature.  In  order  then 
that  we  may  be  able  efficiently  to  utilize  heat  radiations  we 
must  have  first,  a  source  of  easily  controlled  energy  which  can 
readily  be  converted  into  the  energy  of  radiant  heat;  second, 
a  means  of  developing  an  extremely  high  emission  rate  per 
unit  area;  third,  a  means  of  limiting  the  radiation  to  a  small 
area;  and  fourth,  a  properly  shaped  reflecting  surface  of 
material  suitable  for  directing  the  heat  energy  developed  into 
a  beam  of  parallel  rays.  Disregarding  our  primary  assump- 
tion, we  must  in  addition  be  able  to  project  these  rays  upon 
a  swiftly  moving  receptor  at  five  miles  distance  with  sufficient 
effect  to  produce  definite,  mechanical  movements  at  will. 

These  requirements  are  admirably  met  in  our  present  high- 
power  searchlights.  Electricity  as  a  prime  source  of  energy 
lends  itself  easily  to  our  needs  because  of  its  extreme  flexi- 
bility; the  electric  arc  as  a  means  of  transforming  this  energy 
into  heat  is  not  only  extremely  efficient,  but  fulfills  the  require- 
ments of  small  area  and  very  high  temperature  as  well.  The 
energy  in  the  visible  portion  of  the  electric  arc  spectrum  does 
not  exceed  ten  per  cent  of  the  input  energy;  but  with  this  we 
are  not  particularly  concerned,  since  a  " black  body"  receiving 
surface  will  enable  us  to  convert  practically  all  of  the  radiation 
incident  upon  it,  including,  besides  all  of  the  infra-red,  the 
visible,  and  most  of  the  ultra-violet  also. 

The  energy  emission  rate  per  unit  of  area,  which  is  a 
function  of  the  energy  density  per  unit  of  crater  surface,  is 
exceedingly  high;  the  energy  density  may  reach  twenty-one 


INFRA-RED  OR  HEAT  WAVES 


43 


and  one  half  watts  per  square  millimeter,  and  the  temperature 
may  rise  to  the  vicinity  of  three  thousand  eight  hundred 
degrees  Centigrade.  Moreover  the  energy  of  the  high-tem- 
perature portion  is  limited  to  a  comparatively  small  value 
by  the  low  coefficient  of  thermal  conductivity  of  the  electrode 

material.    This  allows  a  suf-    

fluently  close  approach  to 
the. "point  source"  ideal  de- 
sired with  parabolic  re- 
flectors, for  practical  utility. 
Electric  searchlights,  or 
"projectors,"  as  they  are  fre- 
quently called,  have  been 
built  with  parabolic  reflecting 
mirrors  sixty  inches  in  di- 
ameter. Such  a  projector  of 
the  type  used  in  the  United 
States  Navy  is  shown  in  Fig. 
16.  The  power  of  these 
projectors  can  easily  be 
raised  to  fifteen  or  twenty 
kilowatts.  Were  it  necessary, 
heat-wave  generators  of  this 
kind  could  be  constructed 
having  a  capacity  for  trans- 


FIG.  16. 

Sixty-inch  projector  used  with  radio- 
dynamic  torpedoes.  (Published  by  per- 
mission of  General  Electric  Co.) 


forming  an  electrical  energy 

of    one    hundred    kilowatts 

into  the  energy  of  radiant  heat.     The  infra-red  radiations  of 

the  electric  arc  may  be  increased  by  the  addition  of  barium 

chloride  to  the  arc  electrodes. 

Invisibility 

A  searchlight  transmitter  can  be  installed  directly  on  a 
harbor  or  coast  line  and  so  masked  as  to  be  completely  in- 


44  RADIODYNAMICS 

visible  to  ships  several  miles  at  sea.  The  electric  power  would 
preferably  be  generated  at  a  central  power  plant  and  trans- 
mitted over  a  hidden  high-tension  transmission  line  to  a 
number  of  these  hidden  control  stations.  By  means  of  step- 
down  transformers  (and  rotary-converters  if  it  is  necessary  to 
use  direct-current  arcs),  the  high  tension  line  currents  fur- 
nished by  the  central  station  would  be  transformed  to  currents 
of  proper  potential  and  power  for  the  operation  of  the  high- 
power,  electric-arc,  heat-wave  generators. 

Control  operators  at  each  hidden  transmitter  would  be  in 
constant  communication  with  each  other  and  with  the  military 
head  of  the  harbor  defenses  in  order  that  the  control  operations 
might  be  constantly  in  the  hands  of  the  operator  in  the  most 
advantageous  position  with  respect  to  the  attacking  war  vessels. 

Selective  Operation 

Since  heat  waves  as  a  control  agency,  unlike  Hertzian  waves, 
sound  waves,  electromagnetic  and  electrostatic  induction,  or 
earth  conduction,  can  be  directed  at  will,  their  use  demands 
no  consideration  of  the  selectivity  problem,  the  solution  of 
which  has  ever  been  practically  unattainable  under  the  con- 
ditions imposed  in  torpedo  control.  Although  it  is  possible 
to  produce  Hertzian  waves  with  fronts  perpendicular  to  the 
direction  of  propagation,  the  difficulties  involved  in  construct- 
ing reflectors  of  sufficient  size  for  the  wave-lengths  necessary 
are  very  great  from  a  practical  point  of  view.  Other  means 
have  been  developed  for  directing  Hertzian  waves,  among 
which  may  be  mentioned  the  radio-goniometer  of  Bellini  and 
Tosi,  but  in  practice  it  has  been  found  that  the  power  of  such 
transmitters  is  limited. 

In  order  to  prevent  the  enemy  from  projecting  the  beams  of 
their  own  searchlights  onto  the  receiver  of  our  torpedo,  the 
latter  is  provided  with  a  gyroscope  which  serves  to  keep  the 
receiving  heat  detector  always  facing  toward  our  own  trans- 


INFRA-RED  OR  HEAT  WAVES  45 

mitters  on  shore  and  away  from  the  enemy  at  sea,  a  screen  of 
opaque  material  on  the  side  toward  the  sea  providing  means 
cf  intercepting  the  rays  from  the  enemy's  lights.  This  same 
gyroscope  at  night  serves  to  keep  from  the  view  of  the  enemy 
at  sea,  the  screened  signal  lights  on  the  torpedo,  which  at  all 
times  are  plainly  visible  from  shore,  and  which  are  automati- 
cally operated  by  the  control  apparatus  within  the  torpedo. 
Their  purpose  is  to  permit  the  control  operator  on  shore  to 
follow  the  direction  of  the  torpedo  without  keeping  his  trans- 
mitting searchlight  directed  upon  it,  and  thus  in  continuous 
view  of  the  attacking  ships,  and  at  the  same  time  automatically 
to  signal  back  the  operations  occurring  on  the  torpedo. 

The  rays  of  the  searchlight  are  invisible  in  bright  daylight 
unless  an  observer  be  directly  in  their  path ;  this  is  desirable, 
inasmuch  as  it  prevents  the  enemy  from  locating  the  screened 
control  stations.  At  night  the  powerful  light  is  a  distinct 
advantage  in  locating  any  attacking  ships,  and,  when  neces- 
sary, in  following  the  torpedo  itself.  Should  it  become 
necessary  to  have  the  control  station  invisible  during  the  night 
as  well  as  by  day,  suitable  ray  niters  would  be  necessary. 
Substances  which  will  screen  off  or  absorb  the  visible  radia- 
tions and  allow  the  longer  infra-red  waves  to  be  transmitted, 
that  is,  substances  which  are  said  to  be  "diathermanous,"  are: 
black  fluorite,  smoky  quartz,  black  glass,  and  a  strong  solution 
of  iodine  in  carbon  disulphide;  gases  not  near  the  point  of 
condensation  are  also  highly  diathermanous. 

Dispersion  and  Atmospheric  Absorption 

The  best  of  our  present-day  searchlights  are  not  capable  of 
producing  strictly  parallel  rays.  The  non-parallelism  usually 
amounts  to  at  least  three  or  four  degrees.  Because  of  this 
dispersion  the  beam  of  a  searchlight  which  at  the  mirror  is 
sixty  inches  in  diameter,  may  be  five  hundred  or  a  thousand 
feet  in  diameter  at  a  distance  of  five  miles.  It  is  obvious, 


46  RADIODYNAMICS 

therefore,  that  the  illumination  intensity  directly  in  front  of 
the  searchlight  will  bear  to  the  illumination  intensity  at  five 
miles  a  ratio  equal  to  the  ratio  of  the  respective  areas  of  the 
beam  at  these  points;  this  equals  the  ratio  of  the  squares  of 
the  radii  of  the  beam  at  these  points.  In  the  case  of  the  sixty- 
inch  searchlight,  assuming  that  at  five  miles  the  beam  has  a 
diameter  of  one  thousand  feet,  this  ratio  would  roughly  equal 
twenty-five  thousand  to  one.  It  is  possible,  however,  that 
the  dispersion  could  be  reduced  by  a  more  careful  attention  to 
this  useless  waste  of  energy.  No  necessity  has  yet  arisen  for 
such  a  reduction  in  searchlights  as  now  used,  since  it  is  desir- 
able to  illuminate  the  entire  length  of  modern,  five-hundred- 
foot  battleships  at  such  distances. 

Atmospheric  Absorption 

Some  of  the  energy  of  the  rays  is  absorbed  in  the  atmosphere. 
If  the  vibrating  rates  of  the  atmospheric  gases  are  equal  to 
any  of  the  vibration  rates  in  the  projected  waves,  part  of  the 
energy  of  those  particular  waves  will  be  absorbed.  In  this 
connection  it  may  be  possible  so  to  choose  the  electrode 
materials  for  the  arc  that  vibration  rates  produced  in  the  arc 
will  not  be  equal  to  those  of  the  atmospheric  gases,  thereby 
evading  the  energy  losses  due  to  this  cause. 

In  foggy  or  rainy  weather  the  atmospfoeri%  absorption  would 
be  materially  increased  because  water  is  not  very  diather- 
manous.  It  is  also  true,  however,  that  in  such  weathefbattle 
ranges  are  materially  decreased  because  of  the  decrease  in  the 
limit  of  vision,  which,  in  turn,  is  brought  about  by  mist,  rain, 
or  fog.  It  is  difficult  to  foretell  whether  or  not  the  two  would 
decrease  at  the  same  rate. 

Receiving  Radiant  Heat  Detectors 

The  development  of  sensitive  radiant  heat  detectors  has 
followed  several  distinct  lines  corresponding  to  the  varying 


INFRA-RED  OR  HEAT  WAVES  47 

phenomena  of  radiant  energy  in  the  form  of  heat  waves  whose 
lengths  are  longer  than  0.77  ju-  The  length  of  the  visible  waves 
lies  between  0.77  //,  and  0.39  /*,  those  above  0.39  ju  being  in  the 
ultra-violet. 

Those  effects  of  radiant  heat  which  have  been  used  in  the 
production  of  sensitive  detecting  instruments  may  arbitrarily 
be  classified  as  follows: 

i    Volumetric  expansion  (chiefly  of  gases). 

2.  Thermoelectric  currents. 

3.  Resistance  change  in  electrical  conductors. 

4.  Stresses  in  rarefied  gases. 

5.  Linear  expansion  of  solids. 

As  an  example  of  the  first  may  be  mentioned  the  micro- 
radiometer  of  Weber.*  This  instrument  is  a  combination  of 
a  differential  air  thermometer  and  a  Wheatstone  bridge.  A 
thin  glass  tube  which  contains  at  its  center  a  drop  of  mercury 
surrounded  on  both  sides  by  a  solution  of  zinc  sulphate,  con- 
stitutes two  arms  of  the  bridge.  Platinum  electrodes  sealed 
in  the  bulbs  at  each  end  of  the  tube  dip  into  the  zinc  sulphate 
solution.  One  of  the  bulbs,  which  is  made  of  an  opaque 
non-conducting  material,  and  coated  inside  with  lampblack, 
is  fitted  with  a  fluorite  window.  When  radiant  energy  enters 
through  the  non-absorbing,  fluorite  window  it  is  absorbed  by 
the  contained  gas  and  by  the  lampblack.  Thus  heated,  the 
gas  expands  and  pushes  the  liquid  toward  the  opposite  bulb. 
This  changes  the  relative  lengths  of  the  mercury  column  and 
of  the  solution  between  the  platinum  terminals;  the  balance 
of  the  bridge  being  upset,  a  deflection  of  the  galvanometer 
consequently  occurs.  This  instrument  was  stated  to  be 
sensitive  to  a  temperature  change  of  one  millionth  of  one 
degree. 

*  Weber,  Archiv.  Sci.  phys.  et  Nat.  (3)  18,  p.  347;   1887. 


48  RADIODYNAMICS 

Thermoelectric  Detectors 

These  radiant  heat  detectors  may  be  divided  into  two  groups, 
namely,  those  in  which  the  detector  and  the  sensitive  gal- 
vanometer with  which  it  is  used  are  two  separate  and  distinct 
instruments,  and  those  in  which  the  two  are  combined  into 
a  single  instrument.  The  thermopile  is  representative  of  the 
first  group,  and  for  the  second  we  have  the  radiomicrom- 
eter. 

Let  us  first  consider  the  thermopile.  From  the  very  be- 
ginning of  radiant  energy  measurements,  the  power  of  this 
form  of  wave  energy  in  the  ether  for  developing  electric 
currents  in  circuits  containing  junctions  of  dissimilar  metals, 
has  found  wide  application.  Tyndall,  Rubens,  and  other 
pioneers  in  this  domain  secured  very  satisfactory  results  with 
the  thermopile,  in  spite  of  its  great  heat  capacity.  Rubens 
has  described*  a  linear  thermopile  consisting  of  twenty  junc- 
tions of  iron  and  constantin  wires  about  o.i  mm.  to  9.15  mm. 
in  diameter  (resistance  3.5  ohms).  When  used  with  a  gal- 
vanometer having  a  figure  of  merit  of  i  =  i  .4  X  io~10  amperes 
(resistance  =  3  ohms,  period  =  14  seconds),  a  deflection  of 
one  scale  division  indicated  a  temperature  change  of  i°.i  X 
icT6.  A  candle  at  five  meters  gave  a  deflection  of  10  cm.  or 
250  cm.  at  one  meter.  The  area  of  the  exposed  face  of  the  pile 
is  about  1.6  cm.2.  The  heat  capacity  was  such  that  its 
stationary  temperature  was  reached  in  less  than  seven 
seconds. 

If  p  =  the  thermoelectric  power  in  microvolts  per  degree 
( =  53  X  iQ"6  volts  for  iron  and  constantin),  n  =  the  number 
of  junctions  exposed,  and  r  =  the  internal  resistance,  of  the 
thermopile;  and  if  we  combine  the  pile  with  a  galvanometer, 
which,  with  an  internal  resistance  of  w  ohms,  gives  a  deflection 
of  m  millimeters  per  microampere,  then  a  deflection  of  i  mm. 

*  Rubens,  Zs.  fur  Instrumentenkunde,  18,  p.  65;   1898. 


INFRA-RED  OR  HEAT  WAVES  49 

indicates  a  change  in  temperature  at  the  junctions  of  A/  degrees 
when 


npm 

The  highest  efficiency  is  obtained  when  the  resistance  of  the 
thermocouple  is  equal  to  the  combined  resistance  of  the 
connecting  wires  and  of  the  auxiliary  galvanometer. 

Coblentz  has  described*  a  linear  thermopile  of  bismuth- 
silver  junctions  which  had  a  heat  capacity  low  enough  to  attain 
ninety-  two  per  cent  of  its  maximum  temperature  in  two 
seconds.  It  has  a  completely  opaque  surface,  this  novelty 
being  secured  by  a  series  of  overlapping  receivers;  it  has  a  high 
sensitivity;  the  materials  are  sufficiently  strong  to  withstand 
rough  usage;  it  is  quick  acting,  and  yet  sufficiently  massive  to 
permit  operation  in  the  open  without  being  disturbed  by  the 
cooling  effect  of  air  currents. 

The  efficiency  of  the  thermocouple  is  such  that  one  micro- 
watt of  radiant  power  produces  about  0.02  microvolt  per 
thermojunction  in  the  thermopiles  of  bismuth-silver,  or  in 
larger  units  i  watt  =  0.02  volt. 

At  present  we  have  no  exact  knowledge  of  the  mechanical 
equivalent  of  the  radiations  of  large  searchlights,  but  for 
sunlight  we  have  accurate  data.  Upon  the  reasonable  assump- 
tion that  we  can  develop  searchlights  which,  with  the  aid  of 
collecting  and  concentrating  means  at  the  receiver,  will  produce 
received  effects  at  five  miles  equal  to  those  produced  by  sun- 
light without  such  concentrating  means,  we  may  proceed  to 
make  calculations  on  a  sunlight-source  basis.  Mr.  W.  W. 
Coblentz  has  kindly  made  for  the  author  the  following  cal- 
culations on  the  current  developed  in  a  thermocouple  with 
sunlight  as  a  source: 

*  Various  Modifications  of  Bismuth-Silver  Thermopiles  Having  a  Con- 
tinuous Absorbing  Surface,  Scientific  Papers  of  the  Bureau  of  Standards,  No. 
229,  p.  132 


50  RADIODYNAMICS 

The  solar  radiations  reaching  the  earth's  surface  are  about 
i.o  to  1.2  gr.  cal.  cmT2  per  minute  =  gV  gr.  cal.  cm?  sec."1, 
or  about  -^  watt  per  cm.2  per  second.  For  a  quick-acting 
thermopile  the  receiver  has  an  area  of  about  0.04  cmT2,  so  that 
when  exposed  to  sunlight  the  amount  of  radiant  power  inter- 
cepted is 

0.04 

-  =  0.003  watt. 

This  would  produce  0.016  X  0.003  =  4&  X  io~6  volt,  or  a  rise 
in  temperature  of  about  one-half  degree  centigrade. 

By  increasing  the  number  of  couples  to  100  and  placing  the 
whole  in  vacuo,  the  sensitivity  could  be  increased  200  times. 
The  e.m.f.  developed  would  then  be  200  X  48  X  io~6,  or  very 
nearly  o.oi  volt.  Within  recent  years  relays  have  been 
perfected  which  will  operate  with  impressed  voltages  of 
approximately  0.003  vo^-  A  factor  of  safety  is  therefore, 
apparent,  since  the  received  current  is  three  times  that  re- 
quired for  operation.  These  rough  calculations  indicate  that 
heat-wave  control  systems  are  quite  within  the  range  of 
possibility. 

Our  calculations  are  based  on  the  assumption  that  we  can 
produce,  at  five  miles,  thermoelectric  effects  equal  in  magni- 
tude to  the  effects  produced  at  the  earth's  surface  by  the  solar 
radiations.  It  is  probable  that  this  assumption  can  be  realized 
in  practice.  Even  if  this  were  not  possible,  we  have  means  of 
increasing  the  received  effects  so  that  a  much  smaller  heat 
intensity  at  the  receiver  would  produce  the  desired  results. 
The  De  Forest  three-stage  amplifier  is  capable  of  amplifying 
minute  received  currents  to  from  five  hundred  to  a  thousand 
times  their  original  strength.  These  amplifiers  operate  best 
with  pulsating  or  alternating  received  currents.  It  would  be 
a  simple  matter  to  use  a  current  interrupter  of  either  the 
motor-driven  or  vibrating-buzzer  type  for  breaking  up  the 
direct  current  produced  in  the  thermopile.  This  would  intro- 


INFRA-RED  OR  HEAT  WAVES  5 1 

duce  some  complications.  The  thermopile  and  galvanometer 
relay,  with  an  auxiliary  relay  capable  of  handling  larger 
currents  would,  however,  form  a  very  simple  and  reliable 
receiver. 

-  Radiomicrometers,  Bolometers,  and  Radiometers 

Three  other  well-known  types  of  radiation  detectors  are  the 
radiomicrometer,  the  bolometer,  and  the  radiometer.  The 
radiomicrometer,  which  was  invented  independently  by 
d'Arsonval  and  Boys,  consists  essentially  of  a  moving-coil 
galvanometer  of  a  single-loop  with  a  thermo-junction  at  one 
of  its  ends.  It  is,  as  previously  stated,  a  combined  thermo- 
couple and  galvanometer. 

The  bolometer  is  simply  a  Wheatstone  bridge,  two  arms  of 
which  are  made  of  very  thin,  blackened,  metal  strips  of  high 
electrical  resistance  and  high  temperature  coefficient,  one  or 
both  of  which  are  exposed  to  radiation. 

The  radiomicrometer,  because  of  its  great  delicacy,  is  not  so 
suitable  for  radiodynamics  as  the  separate  thermopiles  and 
galvanometer  relays.  The  bolometer  is  an  extremely  sensitive 
radiation  detector,  but  careful  precautions  must  be  observed 
in  keeping  at  a  constant  temperature  the  air  in  which  it  is 
contained  so  as  to  avoid  the  drifting  of  the  zero  position  of  the 
auxiliary  galvanometer. 

The  radiometer  of  Crookes,  a  scientific  toy  which  may  be 
seen  in  many  jeweller's  windows,  has  been  modified  for  radiant 
energy  measurement.  Nichols*  has  described  a  radiometer 
consisting  of  two  blackened  vanes  of  platinum  attached  to  a 
horizontal  arm  and  suspended  in  a  vacuum  by  a  quartz  fiber. 
Although  instruments  of  this  type  will  detect  a  change  in 
temperature  of  one  one-nr'llionth  of  one  degree,  their  extreme 
delicacy  and  sluggishness  make  them  less  suitable  than  ther- 
mopiles for  radiodynamics. 

*  Phys.  Rev.,  4,  p.  297;   1897. 


RADIODYNAMICS 


The  Tasimeter 

Edison's  tasimeter  consists  essentially  of  a  vulcanite  rod  and 
a  microphonic  contact.  The  vulcanite  rod,  which  has  a  high 
coefficient  of  linear  expansion,  is  made  to  exert  a  pressure  on 
the  microphonic  contact  by  means  of  a  screw  press.  A  slight 
expansion  of  the  rod,  brought  about  by  a  slight  increase  in 
temperature,  causes  a  change  in  pressure  on  the  microphonic 
contact,  and  consequently  a  change  in  its  resistance.  When 
the  microphone  forms  one  arm  of  a  Wheatstone  bridge  the 
apparatus  becomes  a  very  sensitive  radiation  detector. 

Edison  used  a  solid  rod  of  hard  rubber  in  compression 
against  two  blocks  of  carbon,  as  shown  in  Fig.  17.  Owing  to 


Compression  Adjustment 


Carbon  Blocks 


ff'IWI'U — 


'•  Hard 'Rubber 
Rod 


FIG.  17. 
Simple  form  of  Edison's  tasimeter. 

the  large  mass  of  rubber  in  the  rod  and  to  the  low  coefficient  of 
conductivity  of  hard  rubber,  this  form  is  sluggish  in  its  action. 
The  author  has  modified  this  instrument  in  order  to  increase 
its  sensitiveness  and  to  decrease  the  period  required  to  attain 
its  maximum  temperature  under  the  action  of  a  given  intensity 
of  received  radiation.  The  modification  consists  substantially 
in  substituting  a  sensitive  telephone  microphone  of  the  carbon 
granule  type  for  the  blocks  of  carbon,  and  in  replacing  the 
hard-rubber  rod  with  a  thin  strip  of  hard  rubber.  This  strip 
is  maintained  in  tension  by  an  adjustable  spring.  The  arrange- 
ment of  microphone,  hard-rubber  strip,  and  adjusting  screws 
is  shown  in  Fig.  18. 


INFRA-RED  OR  HEAT  WAVES 


53 


This  instrument,  when  connected  in  circuit  with  a  battery 
and  ammeter,  will  readily  indicate  a  change  in  current  sufficient 
to  operate  a  relay,  if  influenced  by  the  heat  of  a  bunsen  burner 
at  a  distance  of  one  meter.  Although  not  lacking  in  sensitive- 
ness, heat  detectors  of  this  type  are  subject  to  vibration,  jars, 
and  sounds;  a  weakness  which  disqualifies  them  for  radio- 
dynamics,  particularly  in  the  radiodynamics  of  torpedo  control. 

Thermostats 

In  an  endeavor  to  provide  a  sensitive,  quick-acting,  heat- 
detecting  instrument  which  will  close  a  circuit  directly  without 


FIG.  i 8. 

the  aid  of  a  sensitive  relay,  the  author  has  experimented  with 
various  types  of  thermostats.  After  experimenting  with 
mercury-in-glass  thermostats  designed  especially  for  quick 
action,  with  composite-strip  thermostats  of  both  the  straight 
and  spiral  types,  and  with  alcohol,  mercury,  and  gas  ther- 
mometers, the  conclusion  was  reached  that  a  modification  of 
the  differential  gas  thermometer  would  be  far  more  suitable 
than  the  other  types,  because  of  its  high  sensitiveness  and 
rapidity  of  action. 

The  most  satisfactory  form  thus  far  produced  is  shown  in 
Fig.  19.  The  general  scheme  of  this  type  of  instrument  was 
suggested  to  the  author  by  Prof.  E.  S.  Ferry,  of  Purdue 


54 


RADIODYNAMICS 


University.  In  the  drawing  A  is  the  heat  absorber  of  thin, 
lampblacked  platinum,  B  and  Z>,  two  glass  gas-chambers, 
connected  by  a  glass  tube  of  small  bore;  B  is  lampblacked 
inside.  M  is  a  thread  of  mercury;  W-W  are  water  or  alcohol 
columns  whose  function  is  to  prevent  the  mercury  from  moving 
by  jumps  under  the  action  of  the  expanding  gas  in  B ;  and  C-C 
are  contact  wires  of  platinum  sealed  into  the  glass  tube  so  as 
to  make  contact  with  the  mercury  thread. 

If  heat  rays  fall  upon  the  platinum  disc  A,  they  are  absorbed 
and  their  energy  appears  as  a  rise  in  the  temperature  of  A. 


FIG.  19. 

A  has  a  very  small  heat  capacity  because  of  its  low  specific 
heat  and  its  thinness,  and  it  therefore  requires  but  a  small 
amount  of  heat  energy  to  raise  its  temperature.  Since 
platinum  has  a  high  coefficient  of  thermal  conductivity,  the 
heat  is  rapidly  conducted  to  the  gas  in  the  closed  chamber  B. 
This  chamber  is  so  designed  that  the  distance  from  the  plati- 
num to  any  part  of  the  enclosed  gas  is  small,  in  order  that  the 
conduction-time-lag  through  the  gas  may  be  a  minimum. 
The  inside  of  B  is  lampblacked  in  order  to  prevent  escape  of 
heat  by  radiation  through  its  walls.  The  temperature  of  the 


INFRA-RED  OR  HEAT  WAVES  55 

enclosed  gas  therefore  rises  rapidly  to  the  temperature  of  the 
absorber.  This  gas,  which  is  especially  chosen  for  its  maxi- 
mum coefficient  of  volumetric  expansion  and  its  minimum 
specific  heat,  expands  and  pushes  back  the  liquids  in  the  tube. 
The  mercury  M  will  then  short-circuit  the  two  Connecting 
wires  C-C,  thus  closing  the  external  circuit.  Jf  the  source  of 
heat  be  removed  the  order  of  actions  is  reversed.  The^  ab- 
sorber A  then  becomes  a  rapid  and  efficient  radiator,  and  the 
heat  of  the  gas  in  B  is  dissipated  through  conduction  to  and 
radiation  from  the  platinum  disc  A.  Any  change  in  normal 
temperature,  i.e.,  the  temperature  of  the  air  in  which  both  A 
and  D  are  contained,  will  not  ca'use  any  appreciable  change 
in  position  of  the  mercury  thread  because  pressures  will  be 
produced  in  the  two  gas  chambers  which  are  equal  and  opposite. 

W-W  consist  of  some  non-conducting  liquid  of  low  specific 
gravity.  Without  some  such  steadying  means  the  mercury 
thread  will  have  a  tendency  to  move  in  jumps.  The  specific 
gravity  should  be  low  in  order  that  a  slight  difference  in  the 
levels  of  the  two  columns  will  not  require  a  great  difference  in 
pressure  between  A  and  D.  If  mercury  were  used  a  relatively 
large  difference  in  pressure  between  A  and  D  would  be  neces- 
sary in  order  to  produce  a  motion  of  M  sufficient  to  bridge 
contact  wires  just  above  the  normal  position  of  the  mercury 
surface. 

The  author  has  constructed  thermostats  of  this  type  which 
will  operate  satisfactorily  in  strong  sunlight,  an  exposure  of 
from  one  to  five  seconds  being  sufficient  to  produce  the  maxi- 
mum deflection  of  the  mercury  thread.  The  complete  periods 
were  considerably  less  than  twice  these  values. 

These  results  can  probably  be  improved  upon.  The  author 
has  experimented  with  gases  containing  vapors  of  alcohol, 
ether,  carbon  tetrachloride,  and  similar  liquids  whose  satu- 
rated vapors  have  a  high  coefficient  of  volumetric  expansion. 
The  results  of  these  experiments  are  promising. 


56  RADIODYNAMICS 

A  differential  gas  thermostat  of  this  type,  if  developed  to  the 
proper  sensitiveness,  would  be  as  near  the  ideal  of  a  heat-wave 
receiver  as  we  can  hope  to  reach.  Its  extreme  simplicity  and 
ruggedness,  and  the  absence  of  the  usual  sensitive  relay  are 
its  chief  advantages;  all  other  types  of  receiving  apparatus, 
whatever  the  nature  of  the  control  energy,  require,  besides 
various  other  apparatus,  a  sensitive  relay,  usually  of  the 
galvanometer  type;  this,  in  turn,  requires  a  more  rugged  relay 
for  handling  the  electrical  energy  used  in  performing  the 
various  operations  aboard  torpedoes. 

Heat-wave  control  systems,  we  may  therefore  state,  are 
not  only  within  the  range  of  possibility  but  of  probability  as 
well.  The  extreme  simplicity  and  ruggedness  of  both  trans- 
mitter and  receiver,  the  absence  of  masts  and  other  aerial 
targets,  the  satisfactory  solution  of  the  interference  problem, 
the  near  approach  to  complete  invisibility  of  both  transmitter 
and  torpedo,  and  the  almost  indiscernible  form  of  the  control 
energy  are  factors  that  commend  heat  waves  as  a  connecting 
link  between  the  shore  and  the  wirelessly  directed  torpedo. 


CHAPTER   VIII 
VISIBLE   AND   ULTRA-VIOLET  WAVES 

As  shown  by  the  table,  the  visible  waves  vary  in  frequency 
from  8000  billions  down  to  4000  billions  per  second,  repre- 
senting the  various  colors  from  violet,  down  through  blue, 
green,  and  yellow  to  red,  and  including  all  the  thousands  of 
intermediate  shades.  Quite  apart  from  the  various  optical  and 
chemical  effects  these  waves  are  capable  of  producing,  their 
chief  interest  to  us  lies  in  their  ability  to  effect  changes  in 
the  electrical  characteristics  of  various  substances.  These 
changes  can  be  utilized  for  the  operation  of  delicate  indi- 
cating or  relaying  instruments.  Selenium,  described  more 
fully  in  a  subsequent  chapter,  is  the  most  important  of  these 
substances  affected  by  light.  Systems  of  telegraphy  and 
telephony  based  on  its  peculiar  property  of  changing  its 
electrical  resistance  under  the  influence  of  light,  have  occupied 
the  attention  of  numerous  scientific  men  since  Willoughby 
Smith's  discovery  of  that  property  in  1875.  But  no  ac- 
count of  its  application  to  torpedo  control  can  be  found. 
The  writer  ventures  here  to  present  some  experimental  data 
and  observations  made  by  him,  especially  in  view  of  the 
possible  adoption  of  a  light-wave  selenium  control  system  for 
the  Hammond  dirigible  torpedo. 

From  a  number  of  selenium  cells  of  varying  types  and  re- 
sistances two,  made  by  Dr.  Korn  of  Vienna,  were  chosen. 
The  sunlight  and  dark  resistances  of  one  of  these  were  2000 
and  5200  ohms  respectively;  of  the  other,  1300  and  3000  ohms. 
These  two  cells  were  to  be  used  in  selective  light  telegraphy 
tests  and  it  was  decided  first  to  learn  the  applied  e.m.f. 

57 


58  RADIODYNAMICS 

range  in  which  the  cells  operated  with  the  greatest  sensitive- 
ness and  smallest  inertia.  The  2000-5200  ohm  cell  was  first 
tried.  It  was  connected  in  a  series  circuit  with  a  battery  and 
microammeter,  and  with  a  potentiometer  for  accurate  regu- 
lation of  potentials.  The  operation  was  much  better  with 


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1.4  VOLT  DRY  CELLS 
FIG.  20. 

the  highest  current  density  permissible  with  the  micro- 
ammeter,  so  it  was  decided  to  use  a  milliammeter  and  higher 
potentials.  Potentials  as  high  as  25  volts  were  used  and  the 
results  are  given  in  the  curve  of  Fig.  20.  This  shows  graphi- 
cally the  relation  between  applied  voltage,  current,  resist- 
ance, and  the  current  change  between  light  and  darkness. 


VISIBLE  AND  ULTRA-VIOLET  WAVES  59 

The  current  change  is  the  factor  of  principal  importance.  It 
is  noted  that  this  value  increases  directly  as  the  voltage,  and 
that  the  highest  value  corresponds  to  the  highest  value  of  cur- 
rent density  permissible.  It  was  learned  that  if  this  exceeded 
five  or  six  milliamperes  for  an  hour  or  more,  the  cell  would 
get  out  of  order,  and  a  telephone  inserted  in  the  circuit  in- 
dicated that  the  current  was  varying  at  a  rate  of  several 
thousand  per  second.  The  sound  was  an  irregular  hissing 
or  frying  noise,  resembling  closely  the  sounds  in  a  radio  re- 
ceiver due  to  heavy  atmospherics,  or  that  heard  in  an  ordi- 
nary telephone  during  the  progress  of  a  thunder  storm  in 
the  immediate  vicinity.  The  tests  were  made  with  a  i6-c.p. 
carbon  filament  electric  light,  at  a  distance  of  50  cm. 

The  1300-3000  ohm  cell,  which  we  shall  designate  No.  2, 
was  given  a  similar  test  under  slightly  different  conditions. 
The  i6-c.p.  light  was  placed  at  a  distance  of  10  feet,  and  a 
five-inch  condensing  lens  was  used  to  increase  the  intensity 
of  illumination  on  the  active  surface  of  the  cell.  The  curves 
of  Fig.  21  show  the  relation  between  the  e.m.f.,  current, 
resistance,  and  current  change  with  the  No.  2  cell. 

By  a  comparison  of  Figs.  20  and  21,  it  is  readily  observed 
that  the  combination  of  the  No.  2  cell  with  the  condensing 
lens  was  more  sensitive  at  a  distance  of  10  feet  than  the 
No.  i  cell  at  about  20  inches.  The  indications  of  the  milli- 
ammeter  showed  that  when  the  cells  were  brought  from 
darkness  to  light  the  resistance  dropped  very  quickly  to 
about  two-thirds  the  resistance  change  value,  and  then  to 
the  lowest  value  in  about  five  or  ten  seconds.  From  this 
observation  it  is  obvious  that  the  cell  would  operate  much 
more  efficiently  for  slow  variations  in  the  light  intensity  than 
for  rapid,  such  as  are  used  in  light  telephony,  since  the  lagging 
part  of  the  current  change  represented  by  the  change  occur- 
ring, say  one-fiftieth  of  a  second,  after  a  given  change  in  illumi- 
nation, would  be  of  no  value  where  the  variation  frequency 


6o 


RADIODYNAMICS 


exceeded  50  per  second.  It  would  seem,  therefore,  that  the 
higher  characteristics  of  the  human  voice,  which  may  reach 
vibration  rates  of  five  thousand  per  second,  would  be  re- 
produced with  less  distinctness  than  the  lower  characteristics. 
This  is  actually  the  case  with  light  telephony  as  well  as  with 


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1.4  VOLT  CELLS 
FlG.    21. 

wire  telephony,  the  inertia  being  too  great  to  permit  the  re- 
sistance to  follow  the  rapid  variations  in  the  light's  intensity; 
in  wire  telephony,  however,  the  inertia  is  mechanical  rather 
than  electrical,  except  in  very  long  distance  lines  where 
the  capacity  comes  into  play.  It  was  also  found  that  the 
cells  were  more  sensitive  in  some  parts  of  the  active  surface 


VISIBLE  AND   ULTRA-VIOLET  WAVES  6 1 

than  in  others.  The  five-inch  condensing  lens  was  used  to 
furnish  a  small  spot  of  intense  light  with  which  to  explore 
the  surface  of  the  cell.  When  the  diameter  of  this  spot  was 
made  about  one-sixteenth  of  an  inch  the  best  results  were 
secured.  The  surface  of  the  selenium,  to  secure  this  con- 
dition, was  placed  very  near  the  focal  point  of  the  lens.  The 
sensitive  spots  could  then  be  accurately  located,  and  in  some 
places  the  cell  was  several  times  as  sensitive  as  in  others.  Ex- 
perimental investigations  of  the  cause  of  this  spot  sensitive- 
ness were  not  made. 

A  test  was  made  with  the  No.  2  cell  with  a  view  to  de- 
termine the  possible  value  of  a  selective  light  signalling  and 
radiodynamic  control  system  devised  by  the  writer.  In  these 
tests  a  light  interrupter  was  used  to  effect  the  periodic  illumi- 
nation and  darkening  of  the  selenium  cell  at  rates  up  to  300 
per  second.* 

Fig.  22  illustrates  the  general  arrangement  of  the  apparatus 
as  well  as  the  results  of  the  test.  The  light  used  was  a  4-c.p. 
carbon  filament  electric  lamp,  and  the  interrupter  was,  as 
shown,  similar  to  those  used  on  motion  picture  machines;  it, 
however,  had  a  much  larger  number  of  blades,  and,  as  shown 
in  the  sketch,  was  attached  to  the  shaft  of  a  fan  motor.  A 
rheostat  and  tachometer  permitted  variation  and  exact 
knowledge  of  the  speed,  so  that  any  desired  interruption  fre- 
quency could  be  obtained. 

At  the  receiver  a  three-inch  condensing  lens  was  used  with 
the  selenium  cell.  The  latter  was  connected  in  circuit  with 
a  variable  battery,  a  milliammeter,  and  the  primary  of  a 
ferric  transformer.  The  secondary  of  the  transformer  was 
connected  in  a  series  oscillatory  circuit  with  another  lumped 
inductance  and  variable  capacity  of  the  Korda  type.  By 
varying  the  capacity  or  inductance  of  this  circuit,  it  could  be 

*  In  later  tests  an  arc  light  supplied  with  alternating  current  of  from  60  to 
600  cycles  was  used  to  furnish  the  periodically  fluctuating  light. 


62 


RADIODYNAMICS 


brought  into  resonance  with  the  periodicity  of  the  light  in- 
terruptions. The  oscillatory  currents  set  up  in  this  circuit 
by  the  action  of  the  pulsating  currents  in  the  selenium  cell 
circuit,  when  the  two  were  in  resonant  operation,  were  less 
than  one  ten-millionth  of  an  ampere.  Since  that  value  did 
not  give  a  satisfactory  telephone  signal,  an  amplifying  device, 


60 


Motor       ,/ Light  Interrupter 


Amplifier 


\        ' 
Forced 


I        I 
Resonance 


45 


15 


50  100  ISO          200  250  300  350          400         450 

FREQUENCY 

FIG.  22. 

Resonance  curve  of  the  author's  selenium,  selective,  light-wave,  radiodynamic 

control  system. 

due  to  F.  Lowenstein,  was  used,  which,  in  turn,  effected  the 
operation  of  a  telephone  of  the  high  resistance  type,  and  a 
microammeter.  With  this  arrangement  the  telephone  signals 
received  when  the  circuit  and  light  interrupter  were  in  res- 
onant operation,  were  very  loud,  the  interruptions  of  the 
light  being  heard  as  a  clear  musical  tone,  equal  in  frequency 
to  the  frequency  calculated  from  the  speed  of  the  motor,  and 


VISIBLE  AND   ULTRA-VIOLET  WAVES  63 

the  number  of  blades  on  the  shutter  disc.  The  microam- 
meter  indicated  a  signal  current  of  about  50  microamperes 
as  the  maximum  value  for  resonance  adjustment. 

The  selectivity  was  so  good  that  it  was  difficult  to  keep 
the  apparatus  in  tune,  owing  to  slight  variations  in  the  speed 
of  the  shutter  motor  caused  by  changes  in  the  line  voltage. 
The  resonance  curve  shows  very  clearly  the  degree  of  selec- 
tivity obtained.  It  is  observed  that  when  the  frequency  of 
the  interruptions  was  between  zero  and  about  one  hundred, 
the  selective  circuit  was  forced  to  vibrate  in  its  own  period, 
and  the  effect  on  the  receiving  instrument  was  practically  as 
great  as  when  the  purely  resonant  operation  occurred.  The 
amplitude  of  the  superimposed  fluctuating  current,  on  the 
normal  dark  current  in  the  selenium  cell  circuit,  which  con- 
tained a  considerable  ferric  inductance,  was  probably  50  times 
greater  for  frequencies,  say,  below  100,  than  for  frequencies 
in  the  neighborhood  of  800,  the  natural  frequency  of  the 
circuit  during  the  test.  This  accounts  for  the  fact  that  the 
indicator  currents  were  so  high  with  the  forced  operation  in 
comparison  with  those  of  resonant  operation.  The  funda- 
mental vibration  rate  of  the  circuit  at  this  particular  setting 
was  approximately  345  complete  periods  per  second.  The 
selectivity  no  doubt  could  have  been  improved  upon  by  a 
better  design  of  light  interrupter,  which  would  produce 
sinusoidal  variation  in  the  selenium  cell's  resistance,  and  by 
using  inductances  of  less  resistance  than  were  used  in  this 
experiment. 

Several  electric  lights  in  the  room,  including  a  mercury-arc 
light  and  a  gas  light  placed  directly  between  the  condens- 
ing lens  and  the  four  candle-power  light,  did  not  mate- 
rially affect  the  strength  or  quality  of  the  received  signals. 
It  is  believed  that  the  distance  could  have  been  considerably 
increased  or  the  intensity  of  the  signal  light  reduced  without 
greatly  reducing  the  strength  of  the  received  signals.  The 


64  RA  DIOD  YNA  MICS 

telegraphic  signals  were  sent  with  an  ordinary  Morse  key 
connected  in  series  with  the  signal  light  and  operated  according 
to  the  Morse  or  International  codes. 

Selective  mechanically  tuned  elements  were  also  tried  in 
place  of  the  tuned  electrical  circuit  and  an  even  greater 
degree  of  selectivity  was  obtained.  These  tuned  elements 
were  of  the  different  types  due  to  Ruhmer,  Lowenstein,  and 
Pickard,  and  are  known  as  monotone  amplifones  or  selective 
reed  relays.  A  complete  description  is  not  permissible. 
The  electrical  circuit  is,  however,  to  be  preferred  for  practical 
use  on  account  of  its  nice  adjustability  and  ease  of  handling, 
and  because  it  is  not,  like  the  amplifone,  subject  to  jars  or 
sounds. 

Although  these  experiments  were  rather  encouraging,  later 
tests  made  with  a  24-inch  searchlight  during  both  day  and 
night  furnished  conclusive  evidence  that,  with  the  illumina- 
tion furnished  by  such  a  source  of  light  and  the  best  selenium 
cells  procurable,  the  operative  range  of  such  a  system  would 
not  exceed  a  distance  of  one  mile.  The  tests  were  therefore 
discontinued. 

Ultra-violet  Radiations 

Ultra-violet  light  has  a  powerful  effect  in  facilitating  the 
discharge  of  electrons  from  negatively  charged  conductors  and 
entirely  overcoming  the  hindrance  ordinarily  experienced. 
The  light  waves  may  be  conceived  as  shaking  up  the  neutral 
atoms  condensed  around  the  electrons  and  setting  the  latter 
free. 

Suppose  we  have  two  conductors  in  a  vacuum  at  a  difference 
of  potential  of,  say,  300  volts,  and  that  ultra-violet  rays  are 
made  to  fall  on  the  negative  wire.  The  negative  electrons 
are  set  free  to  enter  the  vacuum  and  are  repelled  by  the 
negative  conductor;  at  the  same  time  they  are  attracted  by 
the  positive  conductor,  and,  since  nothing  prevents  them, 


VISIBLE   AND   ULTRA-VIOLET  WAVES  65 

they  pass  from  one  to  the  other,  and  with  a  velocity  of  ap- 
prpximately  6600  miles  per  second.  (See  Fig.  23.) 

Although  we  have  but  little  data  oh  distances  at  which  these 
effects  are  observable,  we  know  that  they  can  be  brought 
about,  and  a  method  of  applying  this  property  of  ultra-violet 
light  at  once  suggests  itself. 

In  the  "Electrische  Zeitung,"  July,  1898,  Prof.  E.  Zickler 
proposed  to  use  this  property  of  these  radiations  for  teleg- 


•JOOVb/fs- 


Vacuum  Tube 


< 


Ultra  Violet  ftays 


FIG.  23. 

raphy.  He  succeeded  on  a  small  scale  and  believed  that  with 
a  25-ampere  lamp  and  suitable  reflectors,  good  results  were 
possible  over  several  kilometers.  His  proposal  was  based  on 
an  at  first  inexplicable  phenomenon  observed  by  Hertz.  In 
the  course  of  his  experiments  on  resonance  it  was  observed  that 
the  intensity  of  the  sparks  at  the  detector  was  greatly  increased 
by  placing  a  screen  between  it  and  the  exciting  spark.  Later 
the  curious  effect  was  attributed  solely  to  the  ultra-violet 
rays  emitted  by  the  exciting  discharger. 

For  such  simple  apparatus  as  that  required  for  exploding 
mines  where  but  one  energy  impulse  is  required,  the  problem 
is  quite  simple,  requiring  only  an  electric  explosive  cap  in 
series  with  the  battery  and  vacuum  tube.  When  the  rays 
are  directed  upon  the  negative  electrode  of  the  vacuum  tube 
the  discharge  occurs  immediately,  and  the  current  passing 


66  RA  DIOD  YNA  MICS 

through  the  electric  cap  effects  the  ignition  or  detonation  of 
the  explosive  material. 

For  the  control  of  complicated  mechanisms,  however,  a 
relay  and  some  form  of  electric  switching  device  are  required. 

Although  ultra-violet  rays  have  all  the  advantages  of  in- 
audibility, invisibility,  and  simplicity  of  generation  and 
reception,  in  view  of  the  known  fact  that  the  earth's  atmo- 
sphere very  strongly  absorbs  their  power  it  is  very  probable 
that  operation  of  such  a  system  at  useful  distances  would 
involve  considerable  difficulty. 


CHAPTER   IX 
EARTH  CONDUCTION 

The  early  suggestions  of  Steinheil  and  their  subsequent 
application,  as  previously  outlined,  have  been  quite  seriously 
considered  as  a  very  simple  substitute  for  the  comparatively 
complicated  Hertzian  wave  apparatus  for  torpedo  control. 
In  view  of  the  simplicity  of  the  apparatus,  and  of  the  all- 
important  problem  of  selective  control  offered  by  earth  con- 
duction telegraphy,  experiments  were  conducted  by  the  writer 
in  Gloucester  harbor  (1912)  to  determine  roughly  its  value  for 
torpedo  control. 

The  general  plan  of  the  proposed  system  is  shown  graphi- 
cally in  the  accompanying  drawing  (Fig.  24). 

Heavy  insulated  wires  lead  from  the  submerged  plates  to 
the  station,  where,  by  means  of  a  switchboard,  heavy  currents 
can  be  sent  between  any  two  of  the  plates.  The  six  different 
current  fields  thus  capable  of  production  are  shown  in  the 
drawing  by  the  curved  lines. 

The  receiver  comprises  two  conducting  plates,  one  at  the 
bow  of  the  torpedo  and  one  at  or  trailing  behind  its  stern,  with 
insulated  conducting  wires  extending  inside  to  the  terminals 
of  a  sensitive  relay.  The  necessity  of  so  many  current  fields 
is  obvious  when  we  consider  that  we  must  be  able  to  operate 
the  sensitive  relay  regardless  of  the  torpedo's  direction  of 
motion,  i.e.,  the  direction  of  the  current  field  must  correspond 
to  the  direction  of  extension  of  the  receiving  plates.  If  means 
for  accomplishing  this  are  not  provided  it  is  possible  to  lose 
control  of  the  vessel  altogether. 

The  first  thing  to  determine  in  these  experiments  was 

67 


68 


RADIODYNAMICS 


whether  or  not  it  would  be  possible  to  transmit  enough  energy 
to  the  receiver,  at  distances  up  to  the  limit  of  vision,  with 


Submerged 


Submerged 
P/ofe '. 


Submerged 
.'  Plate 


Connecting 
WiretoP/at 


'horeLirre 


Connecting  Wires 
to  PlaJes 


Submerg 
Plate 


Control  Station 
FIG.  24. 


apparatus  of  such  power  as  is  consistent  with  practical  con- 
siderations. With  this  end  in  view,  apparatus  was  arranged 
as  shown  in  the  sketch  (Fig.  25),  which  also  shows  the  received 


20  A  mp. 


^> 

200 


200 


Distance  between  Sending  Pis.  200  Ft. 
-      Receiving  ••       8  Ft. 

, Area  each  -  -     tOSq.Ft. 

• *         "          "  Sending    "    25  "  - 

10       Received  current  values  snown  arelO'fAmpt 

FIG.  25. 


currents  indicated  by  the  Weston  microammeter,  for  different 
positions  of  the  receiving  boat  in  the  current  field.  This  in- 
strument was  connected  directly  between  the  receiving  plates 


EARTH  CONDUCTION  69 

which  were  fastened  at  the  bow  and  stern  of  a  ten-foot  row 
boat. 

The  transmitter  consisted  of  a  25-volt,  1 2o-ampere-hour 
storage  battery  connected  to  two  copper  plates  having  an 
effective  area  of  about  25  square  feet  each.  One  of  these 
plates  was  the  regular  ground  for  the  radio  set  aboard  an  8-ton 
house  boat;  the  other  was  fixed  to  the  bottom  of  a  row  boat, 
moored  about  200  feet  distant. 

A  No.  1 6  bell  wire,  extending  from  the  mast  of  the  house 
boat  down  to  the  row  boat,  served  to  complete  the  circuit. 
The  results  are  clearly  shown  in  the  drawing. 

A  very  curious,  unexplained  phenomenon  was  observed  dur- 
ing these  tests.  The  readings  were  taken  on  transmitted  im- 
pulses of  about  two  seconds  duration,  with  intervening  periods 
of  rest,  and  were  made  in  response  to  signals,  by  an  assistant 
on  the  house  boat,  who  opened  and  closed  the  circuit  between 
the  battery  and  the  overhead  line  wire  extending  to  the  distant 
sending  plate.  In  this  way  one  battery  terminal  was  con- 
tinually connected  to  the  earth  plate  beneath  the  boat. 

In  addition  to  the  usual  earth  current  —  these  currents  may 
be  found  almost  anywhere  on  the  surface  of  this  earth  and 
were  in  this  case  of  course  independent  of  the  sending  battery 
—  readings  were  obtained  which  varied  up  to  50  microamperes 
according  to  the  position  and  direction  of  extension  of  the 
receiving  boat;  and  these  readings  gradually  increased  as  the  re- 
ceiving boat  neared  the  house  boat.  When  the  house  boat  plate 
was  disconnected  from  the  storage  battery  the  received  current 
dropped  to  the  normal  value.  Signals  could  thus  be  sent,  up 
to  distances  of  about  50  feet,  simply  by  making  and  breaking 
the  connection  between  the  battery  and  plate,  with  absolutely 
no  current  flowing  from  the  battery.  The  arrangement  of 
apparatus  and  results  are  shown  in  Fig.  26. 

The  following  day  (Sept.  i,  1912)  further  tests  were  made 
with  increased  power  and  distance.  The  transmitting  current 


70  RADIODYNAMICS 

was  obtained  from  a  bank  of  four  no- volt,  5o-ampere  mer- 
cury-arc rectifiers,  regulated  by  a  series  resistance,  and  meas- 
ured by  an  ammeter.  The  respective  areas  of  the  transmitting 


(< sort 


Copper  Ground 
Plate 


FlG.    26. 


plates  as  well  as  the  distances  between  them  are  given  in  the 
drawing  (Fig.  27).  The  leads  to  the  earth  plates  of  the 
transmitter  were  composed  of  twenty-foot  sections  of  No.  20 
copper  strips,  one  and  a  half  inches  wide,  soldered  together. 


//Ov.  D.C. 


50  Amp. 


400 


100 


400 


'35 


10 


Distance  between  Sending  Plates     400 Ft. 
••  ••          Receiving        "  8  Ft. 

A  rea   each  "  "  8  Sa.  Ft. 

Sending         "  .     SO  &  15  Sq.Ft. 
Received  current  values  shown  are   10'6 Amp. 

FlG.   27. 

The  maximum  current  obtainable  was  50  amperes,  and  the 
received  current  values  shown  were  secured  with  this  trans- 
mitting current. 

On  Oct.  3,  this  distance  was  again  increased,  this  time  to 
approximately  1000  yards  between  the  sending  plates.  Fig. 
28  shows  the  results  of  this  test. 


EARTH  CONDUCTION 


The  received  current  values  resulting  from  these  different 
tests  show  that,  in  a  line  between  the  two  transmitting  plates, 
the  position  of  the  receiving  plates  for  weakest  signals  is 
midway,  and  for  strongest,  nearest  either  of  the  plates.  With 


Distance  between  Sending  Pis.  3000  Ft 
Receiving  ~      30  Ft. 

Area  each  "         -      BSaFt. 

"     .   "  Sending  -    SO  "   "' 

Received  current  values  shown  are  10  Amp 


FIG.  28. 


a  transmitting  power  of  over  five  kilowatts,  the  received 
currents  at  the  position  of  minimum  signal  strength  (which  is 
the  distance  determining  factor),  that  is,  at  a  distance  of  less 
than  one-half  mile,  were  no  more  than  sufficient  to  operate  a 


FIG.  29. 

sensitive  relay  of  the  type  necessary  for  torpedo  control. 
These  results  were  far  from  encouraging  and  the  tests  were 
discontinued. 

A  somewhat  different  scheme  due  to  Mr.  H.  Christian 
Berger,  an  electrical  engineer  of  New  York,  was  next  tried. 
The  transmitting  energy  was  a  high-frequency  oscillatory  cur- 


72  RADIODYNAMICS 

rent,  and  the  receiver  was  of  the  regular  radio  type,  with  two 
earth  connections  instead  of  one  earth  and  one  aerial. 

The  earth  plates  were  of  copper,  100  and  25  square  feet 
area,  respectively,  separated  400  feet,  and  connected,  as  shown, 
in  series  with  the  oscillating  condenser  circuit.  A  hot  wire 
ammeter  in  this  circuit  indicated  a  current  of  four  amperes. 
The  primary  energy  was  delivered  to  the  condenser  circuit  by 
a  3-kw.,  1 10  to  20,000- volt,  6o-cycle  transformer.  (See  Fig.  29.) 

The  receiver  connections,  illustrated  in  the  small  drawing 
at  the  right,  are  those  of  a  common  radiotelegraphic  receiver 
with  the  exception  previously  noted.  The  distance  between 
the  receiver  grounds  was  about  250  feet,  and  the  distance 
between  the  two  sets  of  grounds  of  transmitter  and  receiver 
was  estimated  at  about  500  feet. 

Dr.  L.  W.  Austin,  head  of  the  U.  S.  Radio  Laboratory  in 
Washington,  D.  C.,  has  shown  that  a  radiotelegraphic  sender 
may  exert  a  very  large  amount  of  power  for  the  brief  periods 
of  time  during  which  the  condenser  discharges. 

Considering  a  condenser  of  0.04  mfd.,  charged  to  a  potential 

of  10,000  volts,  Q  is  equal  to  — ^^ —  X  10,000,  or  0.0004 

1,000,000 

coulomb. 

The  work  done  in  charging  such  a  condenser  to  that  poten- 

,.  ,  .  V2C         io,ooo2  X  0.00000004  •     i 

tial  is  equal  to  ,  or  -  — ,  or  2  joules,  or 

2  2 

0.737  X  2  =  1.47  foot-pounds.  It  can  furnish  that  amount 
of  energy  in  one  discharge. 

If  the  condenser  is  discharged  through  a  circuit  of  such  self- 
inductance  as  will  give  a  wave  length  of  1000  meters,  the 
oscillation  frequency  will  be  300,000,  and  the  alternations 
600,000  per  second.  0.0004  coulomb  will  create  an  average 
current  of  0.0004  X  600,000  =  240  amperes.  Were  the  wave 
length  much  shorter  the  current  would  be  correspondingly 
greater,  as  is  shown  by  the  following  example. 


EARTH  CONDUCTION  73 

The  above  condenser  is  discharged  through  an  inductance 
which  will  give  a  wave  length  of  500  meters.  The  alternation 
frequency  of  this  circuit  would  then  be  1,200,000  per  second. 
0.0004  coulomb  will  create  an  average  current  of  0.0004  X 
1,000,000  =  480  amperes.  By  this  we  see  that  the  current 
in  an  oscillatory  circuit  is  inversely  proportional  to  the  wave 
length. 

If  the  energy  of  2  joules  stored  in  the  condenser  is  radiated 
in  five  complete  oscillations,  the  rate  of  doing  work,  if  the  effi- 
ciency of  conversion  is  unity,  is  2  joules  in  -  -  second  = 

600,000 

240,000  per  second  =  240  kw.  This  shows  very  clearly  that 
although  the  available  energy  is  very  small,  the  rate  of  doing 
work,  i.e.,  the  power  of  a  wireless  telegraph  sender,  may  be 
very  great  for  a  short  period  of  time. 

This  peculiarity  of  a  condenser  discharge  is,  no  doubt,  the 
basis  for  Mr.  Berger's  suggestion.  The  scheme  is  distinctly 
novel,  utilizing,  as  it  does,  oscillating  currents  of  high  fre- 
quency, but  with  earth  conduction,  and  not  etheric  radiation, 
as  the  means  of  transferring  the  energy. 

The  tests  given  this  system  were  very  severe  in  that  the 
conditions  imposed  were  far  from  ideal;  but  at  that  time  it 
was  believed  that  if  no  telephone  signals  could  be  received 
under  those  conditions,  the  system  would  be  valueless  for  relay 
operation.  No  signals  were  received  during  this  test  and  the 
experiments  were  discontinued. 


CHAPTER  X 


ELECTROSTATIC    AND    ELECTROMAGNETIC    INDUC- 
TION—HERTZIAN  WAVES 

Following  the  scheme  of  Dolbear,  the  author  experimented 
with  electrostatic  induction  as  a  possible  means  of  torpedo 
control  at  the  Hammond  Radio  Research  Laboratory  in  1912. 

The  transmitter  consisted  of  a  ioo,ooo-volt  transformer, 
especially  built  for  the  purpose,  energized  by  alternating 
current  of  from  60  to  1000  cycles.  One  terminal  of  the 


ill 


Detectoi 


ffeceiver 


FlG.   30. 


secondary  was  grounded,  and  the  other  connected  to  the 
station  antenna,*  which  was  insulated  for  1,000,000  volts  with 
Electrose  strain  insulators. 

The  receiving  apparatus  consisted  of  an  antenna,f  on  the 
house  boat  Pioneer,  connected  to  a  very  sensitive  form  of 
potential  operated  radio  detector  which  will  be  more  fully 
described  in  a  subsequent  chapter. 

Fig.  30  shows  schematically  the  circuit  arrangements. 

*  300  ft.  high,  400  ft.  flat  top.  t  30  ft.  high,  20  ft.  flat  top. 

74 


HERTZIAN  WAVES 


7S 


The  curve,  Fig.  31,  was  made  by  taking  readings  of  the  re- 
ceived currents,  as  indicated  by  a  Weston  microammeter, 
connected  to  the  receiving  detector.  The  Pioneer  was 
started  seaward  within  about  a  hundred  feet  of  the  trans- 
mitting station,  and  readings  taken  every  minute  near  the 
shore;  after  the  steeper  part  of  the  curve  had  been  passed 
the  readings  were  taken  at  longer  intervals. 


1000  2000 

Dl STANCE  IN  FEET 

FIG.  31. 

An  attempt  at  tuning  the  receiver  to  the  frequency  of  the 
alternating  current  used  at  the  transmitter  was  made  by  in- 
troducing a  variable  inductance  of  large  value  and  a  tuning 
condenser  in  series  with  the  antenna,  and  connecting  the  de- 
tector to  a  point  of  maximum  potential  in  this  circuit.  Fig. 
32  shows  this  circuit. 

The  transmitter  was  then  changed  to  the  regular  radio 
type,  the  wave  length  being  pushed  far  beyond  the  natural 
period  of  the  antenna  by  means  of  loading  inductances  in 
both  open  and  closed  circuits.  This  was  done  to  increase 
the  potential  to  the  highest  possible  value,  in  order  to  in- 


76  RADIODYNAM1CS 

crease  the  distance  of  operation.  With  an  emitted  wave 
length  of  about  3000  meters,  the  potential  was  slightly  in- 
creased over  that  previously  obtained  with  the  transformer, 
but  no  material  increase  in  received  results  was  noted. 
The  group  frequency  was  120  per  second.  In  order  to  meas- 
ure the  electrostatic  effects  alone,  no  tuning  to  the  high  fre- 
quency oscillations  was  attempted,  the  receiving  antenna  being 


111 


Antenna 


Iron  Core  Inductance 


Poteritio 
Detector 


-*=  Earth 

FIG.  32. 

connected  only  to  the  detector.  The  low-frequency  tuned 
antenna  circuit  was  then  substituted  for  this  receiver  as  be- 
fore. The  curve  obtained  in  the  best  series  of  tests  (Fig.  31) 
shows  that  with  our  very  sensitive  relay  operating  under 
working  conditions,  the  maximum  range  would  be  only 
up  to  about  1000  feet,  a  distance  far  too  short  for  torpedo 
operation.  This  method  of  control  was  also  abandoned. 

Electromagnetic  Induction 

Beyond  the  work  of  Preece,  Trowbridge,  Edison,  and 
others,  already  mentioned,  very  little  has  been  done  in  the 
field  of  electromagnetic  induction  for  radiodynamics. 

The  fact  that  the  transmitting  and  receiving  coils  or  line 
wires  must  be  in  parallel  planes  is  one  of  the  chief  objections 
to  this  system  for  transmitting  energy  impulses  to  a  movable 
boat. 

The  writer  has  not  been  able  to  find  any  accounts  of  work 


HERTZIAN  WAVES  77 

along  this  line.  Although  the  difficulties  are  not  in  them- 
selves insuperable,  from  a  practical  point  of  view  they  have 
been  considered  too  great  in  comparison  with  other  systems. 
No  effort  therefore  has  been  made  to  utilize  electromagnetic 
induction  as  a  means  of  controlling  dirigible,  self-propelled 
vessels. 

Hertzian  Waves 

Hertzian  waves,  as  every  one  knows  today,  are  by  far  the 
most  important  means  of  wirelessly  transmitting  energy, 
either  for  the  communication  of  intelligence  or  for  the  con- 
trol of  self-acting  apparatus  of  whatever  nature.  We  are 
not  so  much  interested  in  presenting  historical  matter  per- 
taining to  the  very  large  amount  of  work  done  since  Marconi's 
first  experiments;  nor  do  we  wish  to  burden  the  reader  with 
detailed  theoretical  or  practical  considerations  of  the  many 
phases  of  the  radio  signalling  art,  it  being  assumed  that  he  is 
sufficiently  acquainted  with  the  art  as  it  now  stands  to  under- 
stand the  accounts  of  its  special  application  in  the  compara- 
tively new  field  of  radiodynamics;  these  special  applications 
will  be  hereinafter  described  in  sufficient  detail  to  be  readily 
understood  by  those  possessing  some  knowledge  of  electricity. 


CHAPTER   XI 

THE  ADVENT  OF  WIRELESSLY  CONTROLLED 
TORPEDOES 

Although  the  subject  of  this  chapter  does  not  include 
torpedoes  in  general,  it  is  nevertheless  important  to  have 
some  knowledge  of  the  ordinary  torpedo,  and  some  facts 
pertaining  to  its  advantages  and  disadvantages,  if  we  wish  to 
obtain  a  clear  conception  of  the  wirelessly  controlled  weapon 
now  being  perfected  for  modern  naval  warfare. 

The  torpedo  is  claimed  to  be  an  American  invention,  being 
said  to  have  sprung  from  the  fertile  brain  of  Benjamin  Franklin, 
who,  during  the  Revolution,  experimented  with  this  then  un- 
heard of  method  of  marine  attack.  The  first  attempt  in  war 
of  which  we  know  was  made  in  the  harbor  of  Brest,  on  the  west 
coast  of  France,  in  1801,  under  the  orders  of  Napoleon.  This 
first  test  under  actual  war  conditions  was  made  by  an  Ameri- 
can, Robert  Fulton,  the  father  of  steam  navigation.  Fulton 
used  a  submarine  boat,  the  drawings  and  designs  of  which 
have  never  been  published.  He  is  said  to  have  obtained  con- 
siderable success  in  his  experiments,  but  he  failed  in  an 
attempt  to  blow  up  an  English  man-of-war,  whereupon 
Napoleon  withdrew  his  support,  and  the  scheme  was  not 
carried  into  practical  operation. 

We  next  hear  of  torpedoes  in  the  Russian  war  of  1854, 
when  one  of  prodigious  power  was  exploded  in  the  harbor  of 
Cronstadt,  through  copper  wires  connecting  with  a  galvanic 
battery  on  shore. 

Again,  during  our  own  Civil  War,  the  torpedo  made  its 
appearance  in  improved  form.  It  was  employed  for  harbor 

78 


ADVENT  OF   WIRELESSLY  CONTROLLED   TORPEDOES      79 

defense  chiefly  in  and  around  Charleston.  It  was  also  used 
with  deadly  effect  during  the  Spanish-American  War,  and,  in 
the  hands  of  the  Japanese,  inflicted  great  damage  to  the 
Russian  fleet  in  the  battle  of  Fuishima  Straits. 

Every  modern  battleship  is  equipped  with  from  two  to 
four  torpedo  tubes.     The  United  States  alone  has  over  60 


FIG.  33. 
The  first  Holland  submersible. 

torpedo  boat  destroyers,  30  torpedo  boats,  and  50  subma- 
rines, representing  a  cost  of  at  least  fifty  million  dollars  and 
manned  by  over  three  thousand  officers  and  men. 

The  modern  torpedo,  for  the  handling  of  which  all  these 
vessels  have  been  built,  is  about  eight  feet  long  and  nearly 
two  feet  in  diameter  at  the  largest  part.  It  is  propelled  by  a 
compressed-air  motor  fed  from  tanks  containing  air  under 
about  seventy  atmospheres  pressure,  and  is  kept  laterally 


8o 


RADIODYNAMICS 


stable,  and  on  its  intended  course  by  a  gyroscope.     It  has  a 
speed  of  from  twenty-five  to  forty  knots,  a  range  of  from  one 


FIG.  34. 
Types  of  torpedoes. 

thousand  to  four  thousand  yards,  and  carries  from  two  to 
three  hundred  pounds  of  highly  explosive  material,  usually 
gun-cotton.  It  is  launched  from  a  "torpedo  tube,"  a  form 


*";.  35- 
Modern  U.  S.  submarines. 

of  compressed-air  gun,  which  on  battleships  and  submarines 
is  submerged,  and  on  torpedo   boats  and  destroyers  is  so 


ADVENT  OF  WIRELESSLY  CONTROLLED   TORPEDOES      8 1 

mounted  on  deck  that  the  missile  can  be  fired  in  the  desired 
direction  without  swinging  the  ship.     Figs.  33  to  39  will  aid 


FIG.  36. 
View  of  a  battleship  in  a  dry  dock  showing  submerged  torpedo  tube. 

in  making  clearer  the  explanations  relating  to  torpedoes  and 
to  the  different  types  of  ships  upon  which  they  are  used. 


FIG.  37. 
Deck  type  of  torpedo  tube  used  in  launching  torpedoes  from  torpedo  boats. 

Before  actually  firing  a  torpedo  allowances  must  be  care- 
fully made  for  such  variable  factors  as  speed  and  direction  of 


82 


RADIODYNAMICS 


both  the  target  and  the  firing  ship,  the  direction  and  velocity 
of  the  wind,  and  the  condition  of  the  sea. 


FIG.  38. 
U.  S.  S.  South  Carolina  equipped  with  two  submerged  torpedo  tubes. 

The  percentage  of  hits  at  the  extreme  range  of  four  thou- 
sand yards  is  not  greater  than  twenty-five;  and  when  the 
sea  is  disturbed,  even  at  much  shorter  ranges  the  accuracy  is 
still  less. 

The  torpedo  boats  of  both  surface  and  subsurface  types  are 
chiefly  relied  upon  to  do  the  torpedoing,  and,  because  of  the 


FIG.  39. 
Torpedo  boat  destroyer  entering  Norfolk  Navy  Yard. 

fact  that  in  order  to  do  accurate  firing  the  distances  must 
not  be  great,  these  vessels  are  subject  to  the  very  hot  fire 
of  the  enemy's  torpedo  defense  battery  of  three-  and  six-inch 
guns.  The  torpedo  attacks  are,  however,  usually  made  under 


ADVENT  OF   WIRELESSLY  CONTROLLED  TORPEDOES      83 

the  cover  of  darkness  or  fog;  this  fact,  coupled  with  their 
great  speed  and  small  size,  is  their  only  protection.  If  they 
can  approach  near  enough  to  discharge  accurately  a  torpedo 
before  being  discovered  and  illuminated  by  the  searchlights 
of  the  enemy,  all  is  well ;  but  if  not,  it  is  probable  that  their 
thin  hulls  will  be  riddled  with  three-inch  shells  before  they 
can  escape. 

The  principal  advantage  of  the  ordinary  torpedo  is  that 
usually  with  one  well-directed  shot,  a  small,  comparatively 
inexpensive  craft  carrying  from  ten  to  fifty  men  can  totally, 
or  at  least  seriously,  disable  a  huge  fighting  machine  like  a 
modern  dreadnought,  carrying  a  thousand  men  and  costing 
from  five  to  fifteen  million  dollars.  Its  disadvantages  are 
principally  the  great  risk  to  human  life  accompanying  its  use, 
the  comparatively  poor  accuracy  of  the  firing,  and  the  fact 
that  if  a  shot  is  a  failure,  the  five  thousand  dollar  torpedo 
cannot  be  recalled. 

In  the  year  1897,  when  wireless  telegraphy  was  still  in  its 
infancy,  Ernest  Wilson,  an  Englishman,  was  granted  a  British 
patent  on  a  system  for  the  wireless  control  of  dirigible,  self- 
propelled  vessels.  The  primary  object  of  this  invention  was 
to  provide  a  weapon  for  use  in  naval  warfare,  which,  if  in  the 
form  of  a  dirigible  torpedo,  controlled  from  a  shore  or  ship 
wireless  installation,  would  be  most  deadly  in  its  effect  on  a 
hostile  fleet.  No  mention  has  been  found  of  actual  apparatus 
constructed  according  to  Wilson's  plans. 

To  Nikola  Tesla,  probably  more  than  to  any  other  investi- 
gator, belongs  the  credit  of  first  constructing  a  dirigible  vessel 
which  could  be  controlled  from  a  distance  without  connecting 
wires.  His  experiments  were  begun  in  1892  and  from  that  time 
on  he  exhibited  a  number  of  wirelessly-directed  contrivances  in 
his  laboratory  at  35  South  Fifth  Avenue,  New  York  City.  In 
1897  he  constructed  a  complete  automaton  in  the  form  of  a 
boat  (Figs.  40,  41  and  42),  which  would  steer  itself  in  obedience 


RADIODYNAMICS 


to  guiding  impulses  of  Hertzian  waves  sent  out  from  shore. 
On  Nov.  8,  1898,  he  was  granted  a  United  States  patent  on 
this  invention.  In  this  patent  he  mentions  the  use  of  all 


FIG.  40. 

Nikola  Tesla's  telautomaton,  controlled  by  Hertzian  waves,  which  is  the  first 
radiodynamic  boat. 

forms  of  control  energy  including  electromagnetic  induction, 
electrostatic  induction,  conduction  through  earth,  water,  and 
the  upper  atmosphere,  and  all  forms  of  purely  radiant  energy. 


ADVENT  OF  WIRELESSLY  CONTROLLED   TORPEDOES      85 


The  drawings,  of  which  there  are  ten,  illustrate  in  detail  the 
nature  and  arrangement  of  the  apparatus.  These  drawings 
were  made  to  scale  from  the  completed  model,  which  he  had 
in  operation  at  that  time. 


FIG.  41. 
Side  view  of  Tesla's  boat. 

Wilson's  was  the  pioneer  patent  in  that  branch  of  radio- 
telegraphy  now  known  as  radiodynamics.  Since  then  a  large 
number  of  patents  in  this  field  have  been  taken  out  by  various 
inventors,  and  several  of  those  who  have  been  so  fortunate 


FIG.  42. 
Interior  view  of  Tesla's  model  radiodynamic  torpedo. 

as  to  secure  the  means,  have  developed  their  respective  systems 
in  the  effort  to  realize  their  possibilities. 

Gardner  of  England,  Wirth,  Beck  and   Knauss  of  Ger- 
many, Gabet  and  Deveaux  of  France,  Roberts  of  Australia, 


86 


RADIODYNAMICS 


and  Tesla,  Sims,  and  Edison  of  the  United  States  have 
during  the  last  fifteen  years  attempted  to  solve  the  problem  in 
a  practical  way.  All  of  these  investigators  save  Roberts, 
Simms,  and  Edison  have  applied  their  systems  on  boats 
intended  primarily  for  torpedoes,  which  they  control  by 
Hertzian  waves.  Sims  and  Edison,  with  the  cooperation 
of  the  United  States  Government,  developed  a  system  for 


FIG.  43. 
Roberts's  (Australia)  wirelessly  directed  airship  exhibited  in  1912. 

controlling  a  dirigible  torpedo  through  a  trailing  conductor, 
and  Roberts  has  applied  his  system  to  dirigible  balloons.  Fig. 
43  shows  A.  J.  Roberts  and  his  wirelessly-controlled  airship  as 
it  appeared  on  the  lecture  platform.  The  twelve-inch  induc- 
tion-coil transmitter  may  be  seen  at  the  right  on  the  table. 
At  A  is  the  coherer,  tapper,  relay,  and  coherer  battery;  at  B  is 
a  rotary  switch  of  the  Tesla  type;  at  C  are  several  cells  of  a 
storage  battery  and  two  signal  lights;  at  D  are  two  propelling 
and  steering  motors  which  are  mounted  at  the  ends  of  a 


ADVENT  OF  WIRELESSLY  CONTROLLED   TORPEDOES      87 

centrally-pivotted,  horizontal  frame  about  two  feet  long. 
When  both  are  rotating  the  airship  moves  directly  ahead. 
Steering  is  accomplished  by  stopping  one  of  the  motors.  A 
single  wire  about  4  feet  long  serves  as  the  antenna.  The  length 
of  the  airship  is  15  feet  and  the  weight  is  approximately  16 
pounds.  The  gas  bag  consists  of  four  layers  of  pig  intestine. 
The  intestines. of  over  4000  pigs  were  used  in  the  construction 
of  this  bag.  The  maximum  control  distance  is  about  500  feet. 

These  inventors  have  had  various  degrees  of  success  in 
their  endeavors  to  perfect  their  inventions,  but  apparently 
none  have  reached  the  goal.  It  is  true  that  they  have  con- 
trolled the  movements  of  vessels  from  a  distance  without  the 
aid  of  conducting  wires,  but  at  best  the  apparatus  has  worked 
spasmotically,  unsatisfactorily,  and  the  greatest  distance  at 
which  their  vessels  have  been  controlled  has  not  exceeded 
one-half  mile.  But  why,  we  may  ask,  have  these  able  experi- 
menters failed  to  secure  the  desired  results  when  wireless 
telegraphy,  the  mother  of  radiodynamics,  has  made  such 
wonderful  progress? 

OA  analyzing  the  situation  we  find  that  early  in  the  art 
potential-operated  receiving  devices,  such  as  the  coherer,  were 
used,  which  permitted  the  use  of  recording  mechanisms.  As 
the  art  progressed  new  receptive  devices  were  discovered 
which,  in  connection  with  the  marvellously  sensitive  telephone, 
proved  the  coherer  comparatively  insensitive  and  unreliable. 
Coherers  were  then  discarded  and  replaced  by  the  detectors 
and  telephones,  which  provided  a  means  of  signalling  over 
vastly  greater  distances  with  the  same  transmitting  power  as 
before.  The  new  detectors,  while  forming  a  very  desirable 
combination  with  the  telephone,  were  entirely  unsuitable  with 
relays,  and,  therefore,  those  interested  in  the  control  of 
mechanisms  were  compelled  to  retain  the  coherer  as  the 
receiving  detector.  This  is  the  reason  for  the  poor  success 
attained  in  the  field  of  radiodynamics.  The  coherer,  being 


88  RADIODYNAMICS 

capricious  in  its  action,  sometimes  operates  when  the  trans- 
mitting key  is  closed,  and  sometimes  when  no  signals  are  sent, 
possibly  steering  the  boat  to  starboard  when  the  signal  should 
have  turned  her  to  port,  or  stopping  the  engine  when  full  speed 
was  desired.  The  coherer,  because  of  its  unreliability  has 
heretofore  been  the  barrier  to  the  full  realization  of  the  inven- 
tion's possibilities. 


CHAPTER   XII 
SELECTORS 

We  have  already  discussed  the  possible  control  methods  for 
use  in  radiodynamics.  The  function  of  these,  as  has  been 
pointed  out,  is  to  operate  an  electromagnetic  switch,  or  relay, 
as  it  is  called,  from  a  distance.  We  have  also  shown  how  selec- 
tivity in  the  operation  of  a  relay  can  be  secured  by  an  applica- 
tion of  the  familiar  principles  of  resonance;  for  example,  the 
methods  of  tuning  in  radiotelegraphy  to  periodically  recurring 
characteristics  of  the  emitted  wave  energy. 

Since  there  are  a  number  of  mechanisms  to  be  controlled, 
each  with  a  distinct  operation  to  perform  aboard  the  torpedo, 
it  is  evident  that  we  must  have  either  a  separate  receiver  and 
relay  for  each  mechanism,  or  else  some  kind  of  selector  appara- 
tus controlled  by  a  single  receiver  and  relay.  As  pointed  out 
by  Hammond,  we  can,  therefore,  make  two  broad  classifica- 
tions of  the  control  systems,  namely,  (i)  monopulse,  those  in 
which  a  single  kind  of  impulse  controls  a  single  relay,  which, 
in  turn,  controls  a  means  of  selecting  the  desired  circuit,  and 
(2)  polypulse,  those  in  which  a  different  kind  of  impulse  and  a 
separate  receiver  and  relay  are  used  for  each  circuit  to  be 
controlled. 

A  further  classification,  depending  on  the  type  of  relay- 
controlled  selector  used  by  various  experimenters,  follows; 
this  classification  also  has  two  main  heads,  namely,  (a)  those 
systems  involving  the  time  factor  in  impulse  emission,  and 
(b)  those  independent  of  the  time  factor. 

Under  a  we  have: 

(i)  BlondePs,  Gray's,  and  Mercadier's  methods  of  con- 

89 


90  RADIODYNAM1CS 

trolling  separate  mechanisms  by  the  use  of  tuned  mechanical 
or  electrical  elements  at  the  receiver,  and  a  transmitter  capable 
of  transmitting  impulses  of  varying  group  frequency. 

(2)  The  author's  system  which  utilizes  a  method  of  oper- 
ating separate  mechanisms  by  impulses  of  different  length. 

(3)  The  author's  method  of  using  a  transmitter  of  variable 
impulse  frequency  and  a  receiver  with  a  solenoid  of  high  self- 
inductance  in  which  the  current  is  made  to  vary  by  change  of 
impulse  emission  rate  so  that  its  core  can  be  made  to  assume 
any  one  of  a  number  of  positions. 

(4)  Gardner's  system  in  which  the  ratio  between  the  length 
of  impulses  and  of  the  intervening  periods  of  rest  is  varied,  and 
in  which  a  solenoid  is  used  at  the  receiver,  its  core  assuming  a 
definite  position  for  each  value  of  that  ratio. 

Under  b  we  may  place  the  following: 

(1)  Tesla's  method  which  uses  one  type  of  impulse  to  con- 
trol a  number  of  different  mechanisms,  as  a  clock  fitted  with 
a  hand,  which,  operated  from  a  distance,  could  be  made  to  stop 
on  any  five-minute  point,  the  hand  needing  to  pause  say  two 
seconds  before  the  energy  would  be  exerted. 

(2)  Walter's  method,  which  depends  on  synchronous  me- 
chanical rotation;   as  two  clocks,  one  at  the  transmitter  and 
another  at  the  receiver,  each  fitted  with  a  hand,  which  moved 
synchronously  over  their  respective  dials,  and  so  arranged  that 
when  the  transmitting  hand  is  depressed  and  stopped,  say,  at 
the  figure  six,  an  impulse  will  be  sent  out  that  effects  the 
pulling  down  and  stopping  of  the  receiving  hand  which  is  also 
at  six,  thus  closing  the  circuit;   when  the  transmitting  clock 
hand  is  raised,  the  impulse  ceases  and  both  then  resume  their 
synchronous  rotation. 

(3)  There  is  still  another  method  upon  which  modern  auto- 
matic telephone  systems  are  based,  namely,  the  method  of 
closing  any  one  of  a  plurality  of  circuits  by  sending  the  correct 
number  of  impulses;    for  example,  we  have  a  square  figure 


SELECTORS  Ql 

divided  into  100  equal  squares;  beginning  at  the  lower  left- 
hand  square  let  us  number  it  o,  the  next  above  it  i,  the  next  2, 
and  so  on  up  to  9;  then  let  the  square  at  the  right  of  o  be 
called  i,  the  next  beside  it  2,  the  next  3,  and  so  on  to  9;  the 
squares  above  these  are  numbered  in  exactly  the  same  way, 
that  is,  the  columns  are  all  of  the  same  figures.  We  have  a 
checker  normally  at  the  o  position  that  can  only  be  moved 
twice  to  place  it  in  any  square,  and  only  in  two  directions,  i.e., 
up,  and  to  the  side.  Now  in  order  to  get  our  checker  in  space 
67,  for  instance,  we  move  it  six  blocks  up  and  seven  to  the 
side.  In  the  case  of  the  loo-circuit  selector  illustrated  by  this 
checkerboard,  two  different  sets  of  impulses  are  necessary,  one 
which  effects  the  raising  of  the  contact  arm  to  the  desired  row, 
and  another  to  move  it  laterally  to  the  position  desired. 

Among  the  earliest  devices  we  find  that  of  Tesla,  used  also 
by  Orling  and  Braunerhjelm,  Jamieson  and  Trotter,  Roberts, 
and  Varicas,  employing  a  form  of  rotating  commutator  or 
its  equivalent. 

Of  these,  Tesla's,  Varicas',  and  Roberts'  only  have  been 
actually  put  in  practice.  Varicas'  boat  carried  out  in  1901 
the  simple  steering  evolutions  required  but  the  apparatus 
was  quite  unprepared  to  cope  with  intentional  interference. 
Roberts,  as  before  stated,  applied  his  system  in  1912  to  a 
small  dirigible  gas  balloon  for  theatrical  exhibitions.  None  of 
these  operations  were  carried  on  at  any  considerable  distance, 
probably  not  farther  than  a  few  hundred  feet,  but  no  authentic 
data  is  available.  All  employed  the  primitive  filings  coherer. 


CHAPTER   XIII 
EUROPEAN   CONTROL   SYSTEMS 

The  following  extract  from  an  article  on  "  Telemechanical 
Problems  in  the  Wireless  World,"  by  L.  H.  Walter,  M.A., 
taken  with  the  kind  permission  of  the  author,  describes  some 
of  the  systems  experimented  with  in  Europe  during  the  past 
15  years. 

Walter's  Selector  System 

"As  an  example  of  codal  selectors  the  system  devised  by  the 
writer  in  1898  may  be  taken,  not  because  it  is  considered  the 
best  —  for  the  writer  is  prepared  to  admit  that  in  its  early 
form  it  left  something  to  be  desired  —  but  because  it  is 
practically  the  earliest  comprehensive  method,  and  also  be- 
cause it  has  served  as  a  model  upon  which  'numerous  later 
systems  have  been  founded,  such  as  those  due  to  Chimkevitch, 
to  Hiilsmeyer,  Branley  and  others.  The  system  was  worked 
out  as  a  selecting  device  suitable  for  any  telemechanical,  as 
opposed  to  telegraphic  purpose,  although  Righi  and  Dessau 
in  their  'Telegraphic  ohne  Draht/  and  also  Mazzoto  in  his 
book,  describe  the  writer 's  arrangement  as  though  it  were  to 
be  used  for  selective  wireless  telegraphy,  like  the  later  system 
of  Anders  Bull,  which  has  many  points  of  similarity.  The 
original  idea  involved  the  use  of  synchronous  rotating  discs  at 
the  sender  and  receiver,  both  released  by  the  act  of  sending  a 
preliminary  signal.  One  complete  revolution  of  the  disc  then 
resulted,  if  no  further  impulses  were  received,  and  the  arrange- 
ment was  then  in  its  initial  receptive  state.  The  receiver  disc 
comprises  a  number  of  contact  studs  placed  on  the  periphery 

•  92 


EUROPEAN  CONTROL  SYSTEMS  93 

of  the  disc,  corresponding  to  the  code  signal  selected  for  one 
circuit;  these  studs  are  all  connected  with  a  safety  device.  If 
during  the  disc's  rotation  impulses  are  received  when  the 
contact  brush  is  exactly  on  one  of  the  studs  so  connected,  the 
safety  device  has  its  circuit  closer  advanced  one  step  for  each 
such  correctly  timed  impulse,  and  finally  makes  an  operative 
contact  when  the  desired  evolution  (steering,  firing,  etc.)  is 
carried  out.  Should,  however,  any  impulses  arrive  when  the 
brush  is  not  on  a  codal  stud,  the  safety  device  flies  back  to  its 
initial  position,  thus  preventing  the  actuation  of  the  apparatus 
by  unauthorized  or  interfering  impulses.  It  is  well  under- 
stood that  the  transmitter  has  as  many  codal  discs  as  there  are 
circuits  to  be  controlled,  and  there  are  a  corresponding  number 
of  safety  devices.  Special  relays  are  also  used  for  the  purpose 
of  stopping  an  evolution  when  the  next  evolution  is  one  which 
cannot  be  carried  out  without  conflicting  with  the  first  (e.g., 
'helm  to  port'  and  'helm  to  starboard'). 

"  Although  apparatus  of  this  type  was  kept  at  work  in  the 
author's  laboratory  for  several  years  it  has  never  been  fitted 
on  an  actual  boat,  owing  to  the  fact  that  the  idea  appeared  to 
be  before  its  time,  as  people  at  that  date  were  not  inclined  to 
take  even  wireless  telegraphy  very  seriously.  Hiilsmeyer's 
system,  however,  which  dates  from  1906,  and  is  practically 
identical  with  that  of  the  writer,  was  tried  in  Germany  on  a 
practical  scale,  and  is  said  to  have  proved  satisfactory,  al- 
though it  has  not  been  possible  to  obtain  any  further  particu- 
lars. The  much-discussed  system  due  to  Professor  Branley  is 
also  carried  out  on  almost  identical  lines;  his  earlier  arrange- 
ment of  1906  being  later  completed,  in  1907,  by  the  addition 
of  a  safety  device  like  that  of  the  writer." 

Gardner's  Torpedo  Control 

"The  highly  ingenious  system  devised  by  J.  Gardner  ap- 
pears to  have  been  the  first  comprehensive  arrangement  to  be 


94  RADIODYNAMICS 

put  into  operation  on  a  practical  scale,  and  has  proved  to  be 
one  of  the  most  thoroughly  reliable  methods  of  controlling 
vessels  by  means  of  wireless  impulses. 

"At  the  first  glance  the  apparatus,  which  is  based  upon 
an  application  of  Watt's  centrifugal  governor,  appears  to  be 
unlike  any  of  the  other  systems;  but  on  looking  at  it  from 
the  point  of  view  of  a  selecting  system  it  is  clear  that  the 
device  combines  the  properties  peculiar  to  both  the  classes 
as  already  defined.  The  governor,  with  its  hinged  balls 
maintained  near  the  axis  by  means  of  a  spring,  is  normally 
stationary,  in  which  condition  the  sliding  collar  on  the  spindle 
is  in  the  rest  position,  and  all  circuits  are  open.  When  im- 
pulses are  received  from  a  suitable  transmitter,  a  step-by- 
step  arrangement  causes  the  governor  spindle  to  rotate;  the 
governor  balls  tend  to  fly  out  against  the  action  of  the  spring, 
and  the  collar  moves  along  the  spindle,  carrying  with  it  a 
contact  brush  which  is  able  to  pass  over  a  series  of  contacts 
connected  to  the  various  circuits  to  be  controlled.  When  the 
periods  of  impulses  and  no  impulses  are  equal,  the  governor 
maintains  a  constant  speed,  and  it  is  thus  possible,  by  vary- 
ing the  relative  durations  of  the  impulse  periods  and  the 
periods  of  etheric  silence,  to  make  the  contact  brush  pass  on 
to  any  required  contact,  and  to  maintain  it  there.  At  the 
highest  speed  of  rotation  the  firing  contact  is  made. 

"One  of  the  chief  advantages  of  this  system  is  that,  should 
anything  go  wrong,  the  'off'  position  is  reverted  to  auto- 
matically, and  the  torpedo  comes  to  rest. 

"By  the  kindness  of  Mr.  J.  Gardner  the  writer  is  able  to 
give  a  photograph  of  this  interesting  dirigible  torpedo,  which 
is  the  only  British  wirelessly  controlled  craft  that  has  stood 
the  strain  of  actual  tests.  Although  these  trials  were  carried 
out  when  there  was  quite  a  lot  of  shipping  about,  there  has 
never  been  any  mishap  and  this  the  inventor  attributes  to 
the  simple  property  possessed  by  the  system  of  causing  the 


EUROPEAN  CONTROL   SYSTEMS 


95 


96 


RADIODYNAMICS 


vessel  to  rest  when  the  impulses  cease.  The  short  funnel 
which  will  be  noticed  in  the  photograph,  Fig.  44,  is  for  the 
escape  of  battery  gases;  the  aerial  being  supported  from  a 
pole  which  fits  in  the  socket  just  forward  of  the  funnel." 

Deveaux's  Dirigible  Torpedo  Boat 

"The  method  adopted  by  Lalande  and  Deveaux  is  exceed- 
ingly simple,  but  the  boat  represents  the  most  ambitious 
attempt  in  the  history  of  wirelessly  controlled  apparatus. 
The  selector  system  comprises  (i),'  a  circular  distribut- 


FIG. 45- 

ing  switch,  having  on  it  the  studs  pertaining  to  the  cir- 
cuits to  be  controlled;  and  (2),  a  circuit  closer  which  only 
allows  the  current  to  pass  when  the  distributing  switch  arm 
has  reached  the  desired  contact  stud.  In  the  actual  ap- 
paratus the  distributing  switch  has  twelve  studs,  of  which 
nine  lead  to  the  nine  operating  circuits  employed;  the  re- 
maining three  are  distributed  among  the  others  and  con- 
stitute rest  positions  with  a  view  to  saving  the  switch  arm 
from  having  to  execute  a  complete  circle  each  time.  Fig.  45 
is  a  diagram  of  the  connections. 

"In  order  to  carry  out  the  double  function  mentioned,  an 


EUROPEAN  CONTROL  SYSTEMS  97 

electromagnet  M  is  provided  which  moves  forward  by  one 
tooth  at  each  Hertzian  impulse,  a  twelve-toothed  step-by-step 
arrangement  connected  to  the  distributor  arm  D.  During 
the  period  when  this  arm  is  being  advanced,  no  closing  of  the 
operating  circuits  is  possible  owing  to  the  circuit  closer  being 
opened  by  means  of  a  projection  on  the  end  of  the  armature  of 
the  electromagnet;  this  is  shown  at  P.  Thus  if  twelve  im- 
pulses are  received,  the  distributor  would  describe  a  complete 
revolution.  On  the  other  hand,  if  the  impulses  cease  after  the 
distributor  has  been  carried  from  a  rest  stud  to  one  of  the 
operative  studs,  the  circuit  closer  will  complete  the  circuit  after 
a  brief  interval  of  time,  which  is  caused  to  elapse  owing  to  the 
intervention  of  a  retarding  device.  This  latter  consists  of  a 
train  of  clockwork,  which,  by  virtue  of  its  inertia,  does  not 
allow  the  circuit  closer  to  operate  at  once;  a  delay  of  twice 
the  time  required  for  the  distributor  to  be  moved  forward  by 
one  tooth  has  been  found  sufficient.  M.  Deveaux's  paper, 
which  was  published  in  the  Bulletin  of  the  Societe  Inter- 
nationale des  Electriciens,  in  1906,  will  be  found  to  give  full 
information  as  to  the  circuit  arrangements,  but  no  illustra- 
tions of  the  boat  itself. 

"By  the  courtesy  of  M.  Montpellier,  the  editor  of  1'Elec- 
tricien,  the  writer  is  able  to  make  good  this  deficiency,  and 
to  give  two  photographs  of  this  craft;  Fig.  46  shows  the  vessel 
when  hoisted  out  of  the  water,  and  Fig.  47  gives  a  general 
idea  as  to  its  appearance  and  the  visibility  of  its  antenna 
when  afloat;  the  French  cruiser  Saint  Louis,  shown  in  the 
background,  was  watching  the  trials  which  took  place  off 
the  port  of  Antibes  in  the  early  part  of  1906. 

11  The  boat  itself,  which  weighs  6700  kg.,  consists  of  two 
cigar-shaped  bodies  formed  of  steel  plate,  one  above  the 
other  on  the  principle  of  the  Sims-Edison  dirigible  torpedo. 
The  upper  cylinder,  9  meters  long  by  45  cm.  in  diameter,  acts 
as  a  float;  it  is  provided  with  two  small  masts,  which  serve 


98 


RADIODYNAMICS 


i 

I 

I 

.s 
"s 


EUROPEAN  CONTROL  SYSTEMS 


99 


to  support  the  wireless  antenna,  consisting  of  five  wires  kept 
at  a  height  of  about  three  meters;  and  these  masts  have 
lamps  about  halfway  up,  for  the  purpose  of  facilitating 
steering  operations.  The  lower  cylinder  is  n  meters  in 


FIG.  47. 

length,  and  i  meter  in  diameter,  and  contains  the  torpedo- 
ejecting  tube  and  a  Whitehead  torpedo  of  450  mm.  diameter; 
the  accumulator  battery  and  propelling  motors  are  also  con- 
tained therein.  The  control  apparatus  is  intended  to  be 
placed  in  the  lower  cylinder,  where  it  would  be  protected 


100  RADIODYNAMICS 

from  the  enemy's  gunfire  by  two  meters  of  water,  but  in  the 
trials  the  apparatus  was  placed  in  a  sheet  metal  box  on  the 
top  of  the  upper  cylinder  in  order  to  be  available  should  any 
adjustments  be  required.  The  trials  were  carried  out  over 
a  comparatively  short  radius,  400  to  1800  meters,  but  it  is 
stated  that  these  distances  could  easily  have  been  exceeded 
though  to  what  extent  is  not  said. 

"The  transmitting  station  from  which  the  boat's  evolutions 
were  controlled  was  on  land,  and  had  a  five- wire  antenna  15 
meters  in  height;  but  no  information  is  available  as  to  the 
actual  wave  length  employed,  although,  from  the  size  of  the 
receiving  antenna,  it  was  probably  very  short,  of  the  order 
of  80  to  100  meters." 

Wirth,  Beck  and  Knauss 

Remarkable  achievements  in  the  line  of  torpedo  control 
have  been  accomplished  in  Germany,  where  two  unmanned 
motor  boats  33  and  50  feet  in  length  have  been  steered, 
stopped,  started,  and  controlled  in  every  way  by  electric 
waves  transmitted  from  the  shore  without  the  use  of  wires. 
The  system  employed  is  the  invention  of  C.  Wirth  of  Nurem- 
berg. It  has  been  brought  to  its  present  stage  of  develop- 
ment by  several  years  of  experiment,  conducted  by  Wirth 
and  his  cooperators,  the  manufacturer  Beck  and  a  merchant 
named  Knauss;  it  is  protected  by  numerous  German  and 
foreign  patents. 

The  first  success  was  attained  in  1910  with  an  electric 
launch  on  a  lake  near  Nuremberg.  The  vessel  was  33  feet 
long,  and  was  propelled  by  a  5  horse  power  motor,  and  an 
accumulator  battery  of  80  volts  and  300  ampere-hours. 
The  first  public  demonstration  was  given  with  this  boat  in 
1911  before  the  German  Fleet  Club;  in  this  demonstration 
the  unmanned  boat  fired  a  signal  shot  and  then  set  itself  in 
motion.  Travelling  at  a  speed  of  about  10  miles  it  was  made 


EUROPEAN 


101 


to  turn  right  or  left  or  to  stop  completely  and  start  again  by 
the  controlling  operator  in  obedience  to  the  requests  of  mem- 
bers of  the  Fleet  Club.  Each  order  was  obeyed  within  from 
one  to  five  seconds,  and  signal  lights  flashed  back  the  receipt 
of  the  impulses.  The  manuevers  were  continued  for  several 
hours. 

A  boat  50  feet  in  length  was  later  exhibited  in  Berlin,  at 
the  invitation  of  the  German  Fleet  Club.     An  antenna  of 


Explosive  Head 


Receiving  and  Steering  Motor 

Control  Apparatus 


FIG.  48. 
Proposed  form  of  Wirth  radiodynamic  torpedo. 

four  wires  was  stretched  between  the  cupola  of  the  Kaiser 
Pavillion  and  the  restaurant  on  the  shore  of  Lake  Wann. 
The  transmitting  apparatus  which  was  installed  at  the 
restaurant  was  of  the  induction  coil  type,  and  was  of  about 
100  watts  capacity.  The  various  operations  performed  on 
the  boat  were  accomplished  by  sending  impulses  by  means 
of  a  Morse  key.  The  boat  was  equipped  with  an  antenna 
of  four  wires  about  15  feet  high,  a  radio  receiver  capable  of 
adjustment  to  different  wave  lengths  from  the  transmitter,  a 
distributor  or  selector,  electric  steering  apparatus,  signal 
guns,  lights,  and  fireworks  apparatus.  The  tuning  of  the 


102  ;•  L  RA'DtOVYNAMICS 

apparatus  could  be  altered  by  sending  a  long  signal;  this  was 
for  the  purpose  of  evading  interference. 

The  general  scheme  of  the  Wirth  torpedo  is  shown  in 
Fig.  48.  The  diagram  which  is  here  presented  in  Fig.  49 
shows  the  essential  parts  of  the  control  system,  and  the 
circuit  arrangements.  The  coherer  38,  of  the  usual  filings 


FIG.  49. 

type,  is  connected  in  the  circuit  of  the  battery  37  and  a 
sensitive  relay  39.  The  armature  of  this  relay,  36,  serves  to 
close  a  second  circuit  including  the  battery  13,  by  which  the 
electromagnet  14  is  operated.  By  means  of  the  latter,  there 
is  operated  the  lever  8  which  serves  to  rotate  a  ratchet  wheel 
7  by  means  of  a  pawl  in  the  usual  way,  each  time  an  impulse 
is  received ;  at  40  is  a  tapper  for  the  coherer.  Arriving  impulses 
cause  the  ratchet  wheel  to  advance  by  one,  two,  three,  etc.. 


EUROPEAN    CONTROL  SYSTEMS 


I03 


teeth,  and  as  the  wheel  is  mounted  integral  with  a  contact 
disc,  the  latter  is  rotated  at  the  same  time.  The  fixed  brush 
thus  comes  over  a  metal  contactor  or  otherwise  over  the  in- 
sulated part  between  the  contacts  according  to  the  position  of 
the  ratchet  wheel.  Should  there  be  a  contact  piece  under  the 
brush,  the  circuit  of  the  battery  4  is  closed  and  one  of  the 
six  electric  motors,  I-VI  is  set  in  motion.  By  the  rotation 
of  the  motor  there  is  set  working  a  spring  contact  device 
which  will  be  further  mentioned,  and  such  contacts  act  to 


FIG.  50. 

close  the  circuit  of  the  apparatus  which  is  to  be  finally  worked, 
such  as  the  movement  of  the  rudder  of  the  boat,  etc.  A 
second  motor  of  the  series  serves  to  work  another  apparatus, 
and  there  is  used  one  motor  of  small  size  for  each  operation 
to  be  carried  out.  The  purpose  of  the  motors  is  to  furnish 
a  time  element  device,  which  allows  distinction  between  long 
and  short  impulses. 

Fig.  50  shows  the  apparatus  which  is  used  for  two  dis- 
tinct movements,  namely,  for  steering  to  right  or  left.  At  I 
is  a  relay  which  is  worked  by  the  coherer,  and  at  II  the 
contact  disc  before  mentioned.  At  Ilia  and  Illb  are  two 
small  electric  motors  for  making  the  contacts,  this  latter 


104 


RADIODYNAMICS 


being  carried  out  by  the  spring  contact  devices  IVa  and 
IVb,  one  for  each  motor. 

The  coherer  action  sends  current  impulses  by  means  of  the 
relay  I  into  the  electromagnet  of  the  contact  disc.  According 
to  the  number  of  impulses  which  are  sent,  we  have  the  brush 
placed  on  a  metal  contact  or  in  the  insulated  interval.  When 
the  brush  is  on  one  of  the  uneven-numbered  contacts,  the 
motor  Ilia  is  set  working,  and  it  acts  on  the  spring  contact 
device  IVa  so  as  to  operate  the  small  contact  switch  noticed 

at  the  front.  Such  contact 
thus  gives  current  for  op- 
erating the  movement  of 
the  rudder  to  the  left  by  a 
suitable  electromagnetic  de- 
vice. When  the  brush  is 
on  one  of  the  even-num- 
bered contacts  the  motor 
Illb  is  set  running,  and  it 
works  the  corresponding 
spring  switch  IVb  so  as  to 
give  current  for  a  second 
magnetic  device,  for  bring- 
ing the  rudder  to  the  right- 
hand  side.  The  mechanism 
of  the  spring  contact  device 


FIG.  51. 


is  arranged  on  the  retarding  plan,  so  that  it  first  sends  out  a 
wave  signal  which  is  received  at  the  sending  station;  two 
seconds  later  it  closes  the  switch. 

Should  the  brush  remain  but  a  short  time  on  one  of  the 
contacts,  this  will  give  no  effect,  as  the  motor  takes  a  certain 
time  to  start  up,  and  thus  the  motor  gives  a  method  of  work- 
ing by  means  of  long  contacts,  but  not  by  short  ones. 

When  the  brush  is  on  an  insulated  part  of  the  disc  the  de- 
vice is  inactive,  and  the  rudder  comes  automatically  to  the 


EUROPEAN  CONTROL  SYSTEMS 


105 


zero  or  central  position.  The  signal  which  is  sent  back  to 
the  shore  station  is  seen  on  the  paper  strip  of  the  receiver, 
and  the  operator  thus  has  a  check  on  the  working  of  the  ap- 
paratus, and  can  correct  any  wrong  working  by  subsequent 
signals.  Wirth's  transmitting  antenna  is  shown  in  Fig.  51. 

Dr.  E.  Branley's  Control  System 

Dr.  Branley,  of  Paris,  in  addition  to  various  other  kinds  of 
distant  control  apparatus,  devised  an  instrument  with  the 


, 


m 


FIG.  52. 

purpose  of  protecting  the  receiver  against  a  continuous  stream 
of  sparks  such  as  the  enemy  might  send  out  in  time  of  war. 


106  RADIODYNAMICS 

This,  like  a  previous  system  of  Fessenden's,  utilizes  breaks  in 
a  continuous  emission  of  energy  as  the  signal  or  controlling 
impulses,  instead  of  " makes,"  with  periods  of  rest  intervening. 
If  interfering  signals  are  sent  continuously  the  apparatus  can- 
not be  operated  by  any  other  signals,  even  from  the  controlling 
station,  but  should  the  interfering  signals  cease  for  a  short 
time,  the  controlling  operator  can  perform  the  desired  opera- 
tion by  making  the  required  number  of  breaks  in  his  own 
continuous  stream  of  signals. 

Dr.  Branley's  protective  device  consists  of  a  horizontal 
disc  moved  by  clockwork,  and  is  kept  constantly  in  rotation 
first  to  the  right,  then  to  the  left,  by  electromagnets  which 
are  acted  on  by  distant  waves.  The  rotation  of  the  disc 
causes  a  series  of  contacts  for  closing  different  circuits  cor- 
responding to  the  different  operations  to  be  performed.  The 
whole  is  so  arranged  that  when  a  continuous  stream  of  energy 
is  received  the  disc  rotates  forward  and  back.  If  the  dis- 
turbing signals  cease  for  a  brief  period  of  time  the  control 
operator  sends  a  code  signal,  which  acts  upon  the  disc  and  its 
contacts  in  such  a  way  that  the  operation  is  performed. 

In  the  present  type  of  apparatus  the  waves  are  received 
upon  a  new  type  of  coherer  which  is  shown  in  Fig.  52.  It  is  a 
modified  form  of  Dr.  Branley's  tripod  coherer,  and  is  made  up 
of  a  polished  steel  cylinder  at  the  lowest  part.  It  is  fitted  on 
an  upright  support,  and  from  this  three  arms  hang  down  by 
means  of  pivots.  The  arms  carry  well-rounded  steel  projec- 
tions which  bear  lightly  on  the  cylinder  so  as  to  make  the 
coherer  contact.  The  whole  is  enclosed  in  a  vacuum  chamber 
in  order  to  protect  the  coherer  from  the  action  of  the  air. 
Such  a  coherer  is  useless  when  subject  to  vibration. 


CHAPTER   XIV 

WORK   OF  THE  HAMMOND   RADIO   RESEARCH 
LABORATORY 

Following  the  rotary  switch  scheme  of  Tesla,  John  Hays 
Hammond,  Jr.,  head  of  the  Hammond  Radio  Research  Labo- 
ratory at  Gloucester,  Mass.,  began  his  experiments  in  the 
summer  of  1910.  No  detailed  accounts  of  these  first  experi- 
ments are  available,  as  no  systematic  method  of  keeping 
records  of  the  work  had  then  been  inaugurated,  but  it  is 
known  that  mechanisms  designed  to  steer  a  small  boat  were 
operated  at  a  distance  of  three  or  four  hundred  feet.  This 
apparatus,  however,  was  never  actually  used  in  a  boat  for 
steering  purposes. 

During  the  following  winter  an  entirely  new  set  of  control 
apparatus  was  designed  in  New  York  from  Mr.  Hammond's 
plans.  The  object  in  view  was  to  build  a  control  apparatus, 
which  could  be  attached  to  existing  automobile  torpedoes. 
The  coherer  receiving  set,  relays,  rotary  switch,  cut-off  and 
center-stop  mechanism,  and  batteries,  were  all  contained  in  a 
brass  tube  about  one  foot  in  diameter  and  six  feet  long. 

This  apparatus  was  set  up  on  a  float  landing  about  a  thou- 
sand feet  from  the  transmitting  station.  An  antenna  15  feet 
high  and  20  feet  long  was  improvised,  and  after  much  careful 
adjustment,  signals  were  received  which  were  capable  of  start- 
ing, stopping  or  reversing  the  steering  motor.  The  transmit- 
ting antenna  was  of  the  inverted  L-type,  about  80  feet  high 
and  200  feet  long.  An  antenna  current  of  about  2  amperes  was 
registered.  The  transmitting  set  was  of  the  Clapp-Eastham 
type,  60  cycle,  3  kw. 

107 


108  RADIODYNAMICS 

After  these  preliminary  tests  the  apparatus  was  set  up  in 
a  i2-foot  gasoline  launch,  with  a  1 5-foot  antenna  supported 
by  bamboo  poles.  Considerable  trouble  was  experienced  in 
these  tests.  Due  to  the  engine  vibration,  the  sensitiveness  of 
the  Seimmans  and  Halske  relay,  as  well  as  the  Marconi  co- 
herers had  to  be  greatly  reduced.  The  Hertzian  and  inductive 
effects  from  the  gas  engine  caused  considerable  trouble  until 
the  engine  pit  was  entirely  encased  in  sheet  iron;  this,  however, 
did  not  eliminate  the  coherer  trouble  although  it  decreased 
it.  The  instruments  were  almost  inaccessible  for  adjustment; 
the  moist,  salt  air  made  matters  still  worse  by  corroding  the 
multitude  of  contacts.  Finally  a  determined  attempt  at  rudder 
operation  was  made  even  though  the  action  of  the  apparatus 
was  far  from  what  had  been  expected,  and  indeed  necessary. 
The  motor  in  the  tube  was  accordingly  connected  to  the  boat's 
steering  post  by  chain  and  sprockets,  but  when  the  current 
was  switched  on  the  motor  was  found  to  possess  less  than 
half  the  power  required  in  turning  the  rudder  hard  over  when 
the  boat  was  under  way.  Three  weeks  were  spent  in  futile 
attempts  to  eliminate  the  difficulties;  then  the  tube  and  most 
of  its  contents  were  relegated  to  what  was  then  the  scrap  heap, 
and  now  the  historical  collection. 

Simplified  Apparatus 

Plans  were  at  once  formulated  for  the  construction  of  much 
simplified  apparatus,  which  could  be  thoroughly  tested  under 
conditions  in  which  it  could  be  protected  from  the  weather, 
and  observed  and  adjusted  while  in  operation.  An  old  house 
boat  of  about  eight  tons  displacement  fulfilled  all  the  require- 
ments for  a  floating  laboratory  splendidly.  She  was  fitted 
with  a  gasoline  engine  capable  of  driving  her  four  knots  an 
hour,  and  forty-foot  masts  for  supporting  the  antenna.  This 
boat  is  shown  in  Fig.  53. 

Coherers  and  relays  of  highest  sensitiveness  combined  with 


HAMMOND  RADIO  RESEARCH  LABORATORY 


109 


the  necessary  ruggedness  were  secured  from  the  electrical 
instrument  makers  in  America  and  Europe,  A  steering  motor 
of  increased  size  was  procured  and  mechanically  connected 
to  the  steering  wheel  on  the  house  boat  by  a  worm-wheel 
reduction  gear;  a  hand-operated  clutch  permitted  either  radio 
or  manual  control  of  the 
wheel. 

With  this  new  appa- 
ratus installed  in  the 
Pioneer  (as  the  house  boat 
was  afterwards  named), 
where  it  was  protected 
from  the  weather  in  an 
atmosphere  that  could  be 
kept  dry  and  warm  by  a 
coal  stove,  and  arranged 
for  continual  observation 
and  adjustment  while  in 
operation,  the  results  were 
more  satisfactory.  The 
filings  coherer,  however, 
continued  to  be  the  chief 
source  of  our  difficulties. 
Every  known  remedy  for 
the  trouble  was  applied  to 
increase  the  sensitiveness  and  reliability,  but  despite  all  these, 
the  sheet  iron  protection  from  stray  Hertzian  and  inductive 
effects,  the  protective  resistances  and  capacities  for  preventing 
sudden  rise  of  potential  at  current-breaking  points,  —  despite 
the  care  exercised  in  the  selection  and  adjustment  of  jiggers, 
relays,  decoherers,  etc.,  —  the  results  were  so  discouraging  that 
it  was  decided  to  discontinue  the  use  of  the  filings  coherer, 
and  adopt  the  Lodge-Muirhead  mercury-steel-disc  coherer. 
Several  complete  receivers  of  this  type,  which  had  been  dis- 


FIG.  53- 


no 


RADIODYNAMICS 


carded  from  actual  service,  were  purchased  from  the  United 
States  Navy.  These  had  become  obsolete  and  useless  be- 
cause of  the  advent  of  the  telephone  receiving  sets.  The 
best  of  these  was  installed  on  the  Pioneer  and  was  found  to 
be  more  sensitive  and  reliable  than  the  filings  coherer.  Fig.  54 
shows  this  receiver  as  installed  aboard  the  house  boat  and 
Fig.  55  is  a  detail  drawing  of  the  Lodge-Muirhead  coherer. 

After  this  change  had  been  made  the  boat  could  be  kept 
under  fairly  good  control  at  distances  up  to  and  over  a  mile. 
It  was  steered  over  a  prearranged  course  during  both  day 


FIG.  54. 

and  night,  and  in  all  conditions  of  sea  and  weather.  The 
course  was  by  no  means  simple,  covering,  as  it  did,  circles 
around  several  buoys,  and  a  complete  circle  around  the  harbor. 
Fishing  and  other  vessels  were  continually  moving  about  the 
harbor  but  no  great  difficulty  was  experienced  in  avoid- 
ing them,  and,  at  the  same  time,  keeping  on  the  course. 
It  was  found  possible  to  steer  the  boat  against  either  of 
several  upright  spar  buoys  a  mile  from  the  point  of  control. 
At  night  lights,  automatically  controlled  by  the  steering 
mechanism,  kept  the  "helmsman"  at  the  transmitting  key  on 
shore  informed  of  the  boat's  action.  A  white  light  would 
shine  each  time  an  impulse  took  effect;  in  this  way  the  con- 


HAMMOND  RADIO  RESEARCH  LABORATORY 


III 


trol  operator  on  shore  was  immediately  informed  if  the  receiv- 
ing apparatus  or  part  of  the  control  apparatus  had  gotten  out 
of  order.  As  long  as  the  rudder  was  in  the  central  position  no 
lights  save  the  required  running  lights  were  burning.  As  soon, 
however,  as  the  rudder  moved  to  one  side  or  the  other  a  red 
or  green  light  on  the  yard  arm  would  be  connected,  depending 
on  the  resultant  direction  of 
the  boat,  and  this  would  con- 
tinue to  burn  so  long  as  the 
direction  of  the  steering  mo- 
tor's rotation  was  not  reversed. 
When  the  rudder  reached  the 
extreme  hard-over  position  an 
additional  red  or  green  light 
would  flash,  the  two  of  the 
same  color  remaining  illumi- 
nated while  the  boat  was  turn- 
ing in  her  circle  of  shortest 
diameter.  If  the  direction  of 
motion  was  left  then  the  two 
lights  would  be  green  in  color; 
if  right  the  color  would  be  red. 
As  soon  as  the  rudder  was 
again  started  back  to  the  cen- 
ter the  two  lights  would  go 
out  and  a  single  light  of  the 
opposite  color  would  come  on;  when  the  rudder  was  stopped 
at  the  mid-position  by  the  automatic  center-stop  mechanism, 
the  white  light  would  again  flash  for  an  instant,  signifying 
that  fact. 

The  steering  of  the  boat  was  accomplished  by  sending 
Hertzian  wave  impulses,  which,  affecting  suitable  receiving 
and  switching  devices,  controlled  the  one-fourth  horse-power 
electric  motor  mechanically  connected  to  the  steering  wheel. 


FIG.  55. 

A  is  the  steel  disc  with  a  polished 
knife-edge;  B  is  the  small  cistern  of 
mercury  covered  with  a  film  of  oil; 
K  is  a  leather  wiper;  H  and  E  are 
the  terminals. 


112 


RADIODYNAMICS 


The  rudder,  by  this  means,  could  be  made  to  move  to  port  or 
starboard  at  will,  or  set  at  any  intermediate  position  from  the 
transmitting  station. 

During  the  next  year  some  valuable  additions  were  made 
for  carrying  on  the  experimental  and  research  work;   the  size 


FIG.  56. 

of  the  station  was  increased,  two  33O-foot  towers  (see  Figs."  56 
and  57)  were  erected  for  supporting  the  antenna,  a  battery  of 
mercury-arc  rectifiers  was  installed  to  furnish  direct  current 
for  the  operation  of  two  5-kw.  5oo-cycle  motor  generator  sets, 
two  ioo,ooo-cycle  alternators,  a  24-inch  searchlight,  and  vari- 
ous other  apparatus.  A  4o-foot  gasoline  launch  of  150  horse- 
power and  over  25  knots  was  built  for  use  as  a  torpedo,  and 


HAMMOND  RADIO  RESEARCH  LABORATORY  113 


FIG.  57. 
Installing  the  antenna  system  at  the  Hammond  Station. 


FIG.  58. 


RADIODYNAMICS 


FIG.  59. 


other  valuable  additions  were  made  to  the  control  system, 
which  permitted  a  greater  range  and  more  reliable  operation. 

The  battery  of  four  General 
Electric  5o-ampere  recti- 
fiers is  shown  in  Fig.  58. 
Fig.  59  shows  the  5-kw. 
Lowenstein  Transmitter. 

Steering  Apparatus 

A  brief  description  of  the 
control  apparatus  is  here 
necessary  in  order  to  form 
a  clear  conception  of  some 
of  the  important  details. 
It  has  been  previously  mentioned  that  a  control  system  is 
composed  of  two  main  parts:  (i)  the  transmitter  and  receiver, 
and  (2)  the  mechanism  to  be  controlled.  The  principal  parts 
of  the  mechanism,  which  is  the  rudder  control  apparatus,  are 
the  electromagnetically  operated  reversing  switch,  the  steering 
motor,  and  the  source  of  pov.  er. 

The  rotary  switch,  shown  in  Fig.  60,  is  essentially  an 
insulating  drum  fitted  with  contact  pieces;  it  can  be  revolved, 
step  by  step,  through  successive  contact  positions  with  a  set 
of  brushes  by  means  of  an  electrorragnet  and  pawl  and 
ratchet.  The  contact  positions  and  blank  or  "neutral" 
positions  alternate;  moreover,  the  contact  positions  are  of 
two  kinds,  one  for  clockwise  rotation  of  the  motor,  the  other 
for  counterclockwise  rotation.  The  sequence  of  positions, 
then,  as  the  electromagnet  is  impulsively  operated,  is  port, 
neutral,  starboard,  neutral,  port,  neutral,  and  so  on  in  the 
same  order. 

This  is  easily  understood  when  the  rotary  switch  is  looked 
upon  as  a  simple,  double-pole,  double-throw  reversing  switch 
connected  to  the  armature  of  the  steering  motor,  the  shunt 


HAMMOND  RADIO  RESEARCH  LABORATORY  115 

field  of  which  is  continuously  excited.    A  diagram  of  this  con- 
nection is  shown  in  Fig.  61. 

Consider  the  switch  in  the  upper  or  neutral  position,  where 
the  armature  is  disconnected  from  the  source  of  power.     There 


FIG.  60. 

Electrically-operated  rotary  switch  designed  by  the  author  and  used  in  the 
Hammond  System  of  control.  Relay  at  right,  drum  switch  in  the  center, 
and  operating  magnet  at  left.  S 

are  two  possible  ways  of  closing  the  switch,  corresponding  to 
the  two  possible  directions  of  motor  rotation.  One  of  these 
will,  by  swinging  the  rudder  to  port,  cause  the  boat  to  steer 
around  to  port;  the  other  will  effect  starboard  motion.  The 
only  difference  between  these 
two  reversing  switches  is  that 
with  the  hand  type,  the  motor 
after  being  stopped,  can  be 
made  to  run  in  the  same  direc- 
tion again  without  the  necessity  of  passing  over  the  position 
for  opposite  rotation.  With  the  rotary  switch  this  cannot 
be  accomplished  unless  some  auxiliary  instrument  be  used  to 
prevent  the  motor's  rotation  while  passing  over  the  undesired 
position. 


D.C. 


Field 


n6 


RADIODYNAMICS 


The  steering  motor  should  preferably  be  of  the  shunt  type 
with  the  field  winding  continuously  energized.  This  is 
important  to  secure  quick  action.  Motors  larger  than  one- 
fourth  horse-power  cannot  well  be  used  with  such  a  controlling 
switch  because  the  unregulated  starting  current  becomes 
excessively  large.  Where  greater  power  is  required  for  rudder 
operation  a  pneumatic  control  apparatus  is  more  effective. 
The  one-fourth  horse-power  motor  was  found  large  enough  for 
the  33-mile  "  Radio,"  which  had  a  displacement  of  about  four 
tons. 

To  Rotary  -Switch  Magnet 


<?/     A        ,vcv         'Travelling    ''Guide Rod     fytf^top 
^-Starboard  Stop         Block  ,'Adjustmen 

nag     A  djustment 


~6ia*e  Base 
FIG.  62. 


The  source  of  power  is  preferably  a  storage  battery.  It 
should  be  of  the  most  rugged  type.  An  Edison  30-  volt,  120- 
ampere  hour  battery  gave  excellent  service  in  the  Gloucester 
experiments. 

A  crude,  but  nevertheless  operative,  control  system  can  be 
made  up  of  these  essential  parts,  since  with  them  the  steering 
motor,  which  is  mechanically  connected  to  the  steering  wheel, 
can  be  started,  stopped,  and  reversed,  the  worm-wheel  reduc- 
tion gear  serving  to  lock  the  wheel  in  any  desired  position  after 
the  power  has  been  cut  off  from  the  motor.  The  value  and 
reliability  of  such  a  crude  controller,  however,  is  much  increased 


HAMMOND  RADIO  RESEARCH  LABORATORY  117 

by  the  use  of  auxiliary  instruments,  which  make  it  possible  to 
greatly  reduce  the  skill  required  of  the  controlling  operator. 
The  cut-off  and  center-stop  mechanism  is  one  of  these.  It 
consists  essentially  of  a  threaded  shaft  bearing  a  small  traveling 
block,  fitted  with  two  fingers  as  shown  in  Fig.  62.  This  shaft 
is  connected  directly,  or  by  means  of  a  flexible  shaft,  to  the 
reduced-speed  shaft  of  the  steering  motor;  near  each  end  of 
the  worm  shaft  is  a  platinum-tipped  contact  spring.  At  the 
center  is  a  short  stiff  spring  provided  with  a  contact  screw  on 
each  side. 

The  operation  is  as  follows:  The  apparatus  is  so  adjusted 
that  the  central  position  of  the  traveling  block  corresponds  to 
the  central  position  of  the  rudder,  and  the  end  contact  springs 
are  so  placed  that  the  operative  leg  of  the  motor  circuit  is 
broken  by  the  motion  of  the  traveling  block  when  the  rudder 
reaches  the  extreme  right  and  left  positions.  The  center-stop 
contacts  are  engaged  by  the  fingers  on  the  traveling  block  a 
short  time  before  the  rudder  reaches  the  central  position. 
By  closing  the  circuit  of  the  electromagnet  which  operates  the 
rotary  switch,  these  contacts  make  electrical  connections  which 
effect  the  turning  of  the  drum  to  the  neutral  position,  and 
thus  stop  the  motor.  The  adjustment  must  be  very  care- 
fully made  in  order  to  make  the  rudder  stop  at  the  exact 
position  corresponding  to  straight-ahead  motion  of  the 
boat. 

Suppose  the  boat  is  steering  ahead.  An  operator  at  the 
control  station  desiring  to  take  control  depresses  his  key  once, 
the  necessary  length  of  the  impulse  transmitted  being  from 
one-half  to  one  second.  This  impulse  will  move  the  drum  to 
either  a  port  or  starboard  position,  and  is  sent  in  order  to  get 
his  bearings.  Let  us  assume  that  the  boat  immediately  begins 
to  swing  to  starboard.  The  steering  motor  has  been  energized 
and  is  swinging  the  rudder  to  the  right.  The  time  required 
for  the  rudder  to  move  from  the  center  to  either  extreme  posi- 


Il8  RADIODYNAMICS 

tion  is  from  five  to  fifteen  seconds,  depending  on  the  speed  of 
the  steering  motor.  This  time  could  be  fixed  at  any  value 
within  these  limits  by  adjustment  of  the  field  weakening 
rheostat  connected  in  series  with  the  motor's  shunt  field. 

The  operator,  then,  could  allow  the  rudder  to  continue  its 
motion  to  the  extreme  position,  where  it  would  be  automati- 
cally stopped  by  the  cut-off  mechanism,  or  it  could  be  stopped 
at  any  intermediate  position,  by  sending  another  correctly- 
timed  impulse  after  the  first.  This  second  impulse  would 
simply  turn  the  drum  to  the  next  neutral  position  and  thus 
stop  the  motor.  If  he  allowed  the  rudder  to  go  to  the  extreme 
position  the  boat  would  travel  in  its  circle  of  minimum 
diameter  until  the  correct  number  of  impulses  were  sent  to 
change  the  rudder's  position. 

Since  the  drum  was  revolved  to  a  starboard  position  by  the 
first  impulse,  it  remains  there,  the  motor  circuit  for  starboard 
rotation  being  opened  by  the  cut-off  mechanism.  Obviously, 
then,  two  impulses  are  required  to  rotate  the  drum  to  the  next 
port  position.  If  these  are  sent,  the  motor  will  rotate  in  the 
opposite  direction,  and,  if  no  more  impulses  are  sent  within 
the  fixed  time  limit,  the  rudder  will  move  to  the  central  posi- 
tion and  automatically  stop.  This  central  stop,  as  before 
explained,  is  effected  by  the  automatic  rotation  of  the  drum 
to  a  neutral  position.  Remembering,  then,  that  in  this  case 
the  neutral  position  is  followed  by  a  starboard  position,  one 
impulse  will  send  the  boat  to  starboard  again  and  the  minimum 
number  of  impulses  for  port  steering  is  three.  If  these  are 
transmitted,  the  rudder  will  turn  to  the  extreme  port,  unless 
stopped  at  some  intermediate  position,  by  sending  an  additional 
impulse. 

It  is  thus  seen  that  the  nucleus  of  the  apparatus  is  simply  a 
wirelessly-operated  switch,  supplemented  by  auxiliary  ap- 
paratus, which  automatically  perform  operations  that  would 
be  very  difficult  for  the  distant  operator. 


HAMMOND  RADIO  RESEARCH  LABORATORY  IIQ 

In  practice  a  difficulty  developed  which  was  only  overcome 
after  considerable  experimentation.  It  was  found  that,  when 
the  rudder  and  traveling  block  were  in  their  central  positions, 
and  three  impulses  were  sent  at  the  maximum  speed  permitted 
by  the  inertia  of  the  various  parts,  the  drum  remained  on  the 
undesired  contact  long  enough  to  allow  a  considerable  number 
of  revolutions  of  the  steering  motor  in  the  direction  opposite  to 
that  desired.  The  following  would  be  the  result : 

The  first  impulse  would  effect  rotation  in  the  wrong  direc- 
tion, the  motion  of  the  traveling  block  being  great  enough 
to  allow  the  contact  finger  to  pass  under  the  spring.  The 
second  impulse  would  bring  the  next  blank  space  into  posi- 
tion, stopping  the  block's  motion;  the  third  would  effect  the 
desired  rudder  motion  and  the  block  would  immediately  begin 
to  move  with  the  rudder  in  the  desired  direction.  After  a  few 
revolutions,  however,  the  center-stop  finger  would  engage  its 
contacts,  and  as  a  result  the  motor  would  stop. 

In  this  way  it  was  found  impossible  to  get  the  rudder 
through  the  central  position  from  one  side  to  the  other. 
Tests  without  the  automatic  stop,  however,  clearly  indicated 
the  futility  of  trying  to  dispose  of  it,  —  it  being  found  im- 
possible to  steer  a  straight  course  because  of  the  difficulty  of 
stopping  the  rudder  at  the  exact  point  necessary  for  steering 
directly  ahead. 

Attempts  were  made  to  surmount  this  difficulty  by  the 
introduction  of  considerable  inertia  into  the  rotating  parts 
connected  to  the  motor,  so  that  in  the  brief  interval  of  time 
necessary  in  passing  over  undesired  operative  positions  of  the 
rotary  switch,  the  motor  could  not  develop  enough  speed  to 
cause  the  above-mentioned  difficulty.  This  was  partially 
satisfactory,  but  did  not  completely  solve  the  problem. 

The  solution  was  finally  found  in  a  "time  relay,"  especially 
built  for  this  purpose  after  our  plans,  in  New  York.  This 
instrument  consists  principally  of  an  iron-clad  solenoid  with 


120 


RADIODYNAMICS 


a  movable  core,  and  an  adjustable  air  dash  pot.     A  plan  view 
of  this  relay  is  shown  in  Fig.  63. 

When  energized,  the  core  is  drawn  up  in  a  period  of  time  that 
can  be  easily  varied,  by  adjustment  of  a  thumbscrew,  from  a 
fifth  of  a  second  to  ten  seconds.  A  set  of  heavy  platinum  con- 
tacts is  fixed  on  the  core  and  an  adjustable  screw  so  that  a  local 
circuit,  carrying  ten  or  fifteen  amperes  can  be  satisfactorily 
opened  and  closed  at  the  end  of  the  "in"  stroke.  A  light 
spring  serves  quickly  to  bring  the  core  back  to  the  normal 
position  after  the  solenoid  is  de-energized.  This  is  facilitated 


Field  Frame 


Back  Spring  Co// 


Solenoid 


....  to"--- 

FIG.  63. 


by  a  one-way  valve  which  permits  the  expulsion  of.  the  air  in 
the  dash  pot  with  but  little  retardation  on  the  return  stroke. 
The  solenoid  windings  were  connected  in  parallel  with  the 
electromagnet  of  the  rotary  switch,  and  the  contacts  were 
connected  in  one  leg  of  the  battery  circuit  to  the  motor 
armature.  By  this  means  the  motor  armature  current  could 
not  be  exerted  until  a  definite  length  of  time  had  elapsed 
after  the  impulse  had  been  sent,  and  thus  the  undesired  oper- 
ative positions  on  the  drum  switch  could  be  passed  over 
without  difficulty.  The  time  limit  was  usually  set  at  about 
one  second.  Another  time  relay  of  the  same  kind  was  used 
for  engine  control.  In  this  way  short  impulses  of  about  one- 


HAMMOND  RADIO  RESEARCH  LABORATORY 


121 


half  second  duration  were  used  for  steering,  and  long  im- 
pulses of  about  ten  seconds  were  used  for  starting  or  stopping 
the  engine.  The  engine  control  in  these  experiments  was 
effected  by  opening  or  closing  the  ignition  circuit,  the  engine 
being  so  adjusted  that  it  would  stop  at  the  required  point  at 
which  the  explosions  occur.  It  was  found  possible  to  start 
the  engine  in  this  way  as  long  as  an  hour  after  it  had  been 
stopped.  This  second  time  relay  was  also  used  for  firing  ex- 


LU 


Rotary  Switch  Magnet 


Potenfio        Sensitive  Relay 
Detector     •'  •  • 

I1! 


'"•-£  oadinc/  Inductance 
—Tuning  Capacity 


Time  Relay 
for  Engine  Control ' 


Rotary  Switch 
/    Connections 


io  cnqi 
Clutcfi- 


FlG.   64. 


plosive  charges  of  powder  placed  on  top  of  the  boat's  cabin. 
The  complete  circuit  is  shown  in  Fig.  64. 

During  the  summer  and  autumn  of  1912,  with  this  im- 
proved apparatus,  the  results  were  very  encouraging.  The 
25-knot  Radio  of  which  Fig.  65  is  a  reproduction  was  con- 
trolled with  reliability  and  precision  at  ranges  of  over  three 
miles,  a  distance  far  in  excess  of  that  attained  by  European 
investigators.  Demonstrations  made  before  the  U.  S.  War 
Department  authorities  proved  beyond  a  doubt  that  the 
dirigible  torpedo  would  be  of  great  use  in  naval  warfare, 
especially  for  coast  defense. 


122  RADIOD  YNA  MICS 

The  operations  can  be  carried  on  at  night  almost  as  well  as 
by  day.  With  a  special  reflector  of  the  triple-mirror  type, 
and  a  searchlight,  the  maneuvers  of  the  boat  can  be  followed 
with  ease  from  the  control  point,  although  from  any  other 
position  the  reflected  light,  and  the  boat  itself,  are  practically 
invisible. 

The  broad  idea  of  the  Hammond  torpedo  control  system 
for  coast  defense  is  this: 

One  powerful  transmitting  station  is  employed  and  suitably 
placed  in  some  protected  situation  with  respect  to  the  gunfire 


FIG.  65. 

of  the  enemy.  A  number  of  operators  are  placed  along  the 
shore;  these  different  operators  have  wire  connection  with 
the  wireless  station  and  telephone  connection  with  one 
another.  A  number  of  torpedoes  may  be  used,  each  of  which  is 
controlled  by  an  impulse  of  specific  characteristics.  These 
are  moored  at  a  central  protected  torpedo  base,  and  one  or 
more  can  be  controlled  at  the  same  time  by  either  of  the 
operators  at  the  hidden  control  stations.  The  torpedoes  are 
started  at  the  base  and  passed  on  to  the  control  of  the  oper- 
ators in  the  most  advantageous  positions,  who  operate  under 
orders  transmitted  over  the  telephone  lines  by  the  military 


HAMMOND  RADIO  RESEARCH  LABORATORY  123 

head  of  the  fortifications.  The  wireless  station  is  equipped 
with  a  wave  generator  for  each  torpedo,  and  by  means  of  the 
wire  connections,  which  extend  from  the  control  point  to 
the  central  station,  impulses  can  be  sent  from  either  of  these 
generators  by  either  of  the  control  operators. 


CHAPTER   XV 


THE   SOLUTION   OF   THE   PROBLEMS   RELATED    TO 
BATTLE-RANGE   TORPEDO    CONTROL 

The  problem  of  performing  a  number  of  operations  aboard 
a  moving  vessel  at  distances  of  over  a  mile  is  by  no  means  a 


120 


Galena, 
Y 


RECEJ.VER 


1300m. 


\SOO-~-~. 


^    TRANSMITTER 

U  i       i       I 

_L  'HWA.-IOAmps. 


Distance- intensity  received  current 

on  "D/RIGIA"  with    Solid- Rectifier'  Detectors 


ZQ  30 

MINUTES 
3 

MILE.S. 

FIG.  66. 


simple  one,  even  from  a  theoretical  point  of  view.  It  might 
be  mentioned  that  controlling  a  number  of  mechanisms  with 
but  a  single  relay  is  easy  in  comparison  with  wirelessly  con- 

124 


BATTLE-RANGE   TORPEDO  CONTROL  125 

trolling  a  relay  five  miles  away,  which  at  the  same  time  is 
immune  from  accidental  or  intentional  interference  from 
other  sources  of  energy.  Then,  too,  when  we  reflect  that 
probably  less  than  one-billionth  of  the  energy  radiated  into 
space  by  the  transmitter  reaches  the  receiver,  the  quanti- 
tative aspects  of  the  problem  begin  to  come  into  evidence. 

Fig.  66  is  a  graphical  representation  of  the  current  re- 
ceived on  board  the  Pioneer,  which  was  first  used  as  a  torpedo 
in  the  Gloucester  experiments.  The  transmitting  energy  in 
the  antenna  *  was  about  two  kilowatts  at  a  wave  length  of 
approximately  1300  meters.  The  group  frequency  was  1000 
and,  with  the  air  cooled  quenched  spark  gap,  and  loose  in- 
ductive coupling  between  the  open  and  closed  oscillatory 
circuits,  the  decrement  was 
fairly  low. 

The  receiving  antenna  as 
shown  in  the  illustration 
of  the  Pioneer  was  of  the 
inverted  L  type,  30  feet 
high  and  with  a  2o-foot 
flat  top,  the  detector  was  FIG>  57. 

one  of  the   solid   rectifier 

type,  essentially  a  crystal  of  galena  with  a  light  spring 
contact.  It  is  shown  in  Fig.  67  and  was  designed  by  the 
author.  The  current  values  given  were  read  directly  upon 
a  Weston  microammeter.  The  readings  were  taken  at  five- 
minute  intervals,  except  in  close  proximity  to  the  station, 
and  the  distances  corresponding  to  these  intervals  were 
computed  from  the  boat's  speed  and  log  readings.  This 
curve  shows  how  quickly  the  received  current  drops  down 
within  a  mile,  and  how  it  remains  almost  constant  after  this 
distance  is  well  passed.  The  high  value  of  the  received  cur- 
rent within  a  short  distance  of  the  transmitter  may  be 

*  300  ft.  high,  400  ft.  flat  top. 


126  RADIODYNAMICS 

due  to  the  augmentation  of  the  Hertzian  effects  by  the  purely 
electrostatic  effects,  as  evidenced  by  the  curve  made  in  the 
experiments  with  an  electrostatic  telegraph  (Fig.  20).  The 
received  current  at  three  miles  was  only  about  3-icr6  amperes. 
So  far  as  we  were  able  to  learn  there  was  no  relay,  possessing  the 
necessary  mechanical  and  electrical  stability,  which  was  sensi- 
tive enough  to  operate  reliably  on  such  a  small  amount  of 
energy.  The  most  sensitive  relay  we  could  procure  in  the 
United  States  and  Europe,  which  was  rugged  enough  to 
operate  reliably  under  the  conditions  of  shock  and  vibration 
aboard  a  small  high-speed  boat  in  a  rough  sea,  required  about 
300.  icr6  amperes.  We  had  as  high  a  transmitting  antenna 
as  was  practicable,  the  most  efficient  transmitting  apparatus, 
and  the  most  sensitive  receiving  set  obtainable,  and  yet  the 

breach  between  the  available 
and  the  required  received  cur- 
rent, was  so  wide  that  it  ap- 
peared almost  impossible  to 
bridge  it.  With  a  sender  that 
could  deliver  only  one  mi- 
croampere at  four  miles,  and  a 
receiving  relay  that  required 
300  microamperes  for  opera- 
tion, the  problem  was  a  serious 
and  discouraging  one. 

FKJ  68  The  first  step  in  the  solu- 

tion was  in  the  improvement 

of  the  sensitive  relay.  This  was  of  the  Weston  pivoted  galva- 
nometer type,  and  is  reproduced  in  Fig.  68  by  the  courtesy  of 
the  Weston  Electrical  Instrument  Company.  The  permanent 
magnet  was  replaced  by  an  electromagnet,  which,  by  increasing 
the  field  intensity,  more  than  doubled  the  sensitiveness.  Fig. 
69  shows  graphically  the  effect  of  variation  in  the  field  energiz- 
ing current.  Later  the  author  replaced  the  delicate  platinum 


BATTLE-RANGE   TORPEDO  CONTROL 


127 


contacts  by  a  single  platinum  point  on  the  movable  arm, 
and  an  adjustable  globule  of  mercury.  This  increased  the 
operating  sensitiveness  from  twenty  to  thirty  times,  for  only 
an  extremely  small  contact  pressure  was  required  to  keep  the 
circuit  closed  under  considerable  vibration.  These  relay  im- 
provements therefore  increased  the  receiver's  sensitiveness 
about  fifty  times. 


100 


Sensitiveness  Curve  of 
Remodelled  Wesfon  Galvanometer 

r-^- 


2  4  e 

FIELD  CURRENT  AMPS. 

FIG.  69. 


Fig.  70  is  a  plan  view  of  this  improved  sensitive  relay. 
T  and  Ti  are  terminals  of  electromagnet  windings,  W  and 
Wi,  surrounding  soft  iron  cores.  When  in  operation  T  and 
Ti  are  connected  to  a  source  of  direct  current.  T2  and  T3 
are  terminals  of  movable  coil  C,  the  pivots  and  mountings  of 
which  are  not  shown.  B  is  a  light  arm  fixed  to  C.  Terminal 
T4  is  connected  to  arm  B.  L  is  a  non-oxidizable  contact 
piece  fixed  to  B.  M  is  the  top  of  a  column  of  mercury  ex- 
tending into  and  above  the  block  H.  The  size  of  the  globule 


128 


RADIODYNAMICS 


M  above  H  is  adjustable  by  screw  S.  The  distance  of  M 
from  L  in  its  normal  inoperative  position  may  be  varied  by 
the  adjusting  screw  Si. 

Ordinary  instruments  of  this  kind  have  permanent  magnets, 
but  by  the  use  of  electromagnets  and  suitably  shaped  pole 
pieces,  a  much  more  intense  field,  and  consequently  a  greater 
sensitiveness,  could  be  secured. 


FIG.  70. 

When  C  is  energized  by  current  flowing  in  the  right  direc- 
tion, arm  B  carrying  contact  L  will  move  toward  M.  L  will 
make  contact  with  and  move  into  M  and  establish  a  good 
low-resistance  connection  in  the  local  circuit  connected  to  T4 
and  T5.  When  C  is  de-energized,  the  spiral  spring  Q  causes 
B  to  return  to  the  normal  position.  With  a  relay  of  this 
description  currents  of  a  few  microamperes  could  be  relayed 
under  conditions  of  vibration  which  necessitated  a  current  of 
a  hundred  microamperes  with  the  best  of  ordinary  sensitive 
relays  of  the  solid  contact  type. 


BATTLE-RANGE   TORPEDO  CONTROL 


129 


The  next  step  in  the  solution  of  the  control  problem  was 
to  discard  the  Lodge-Muirhead  coherer,  and  to  adopt  the 
vacuum-tube  rectifier,  which  was  perfected  in  this  country 
by  DeForest.  This  is  about  twice  as  sensitive  as  the  best 
solid  or  electrolytic  rectifiers,  and  has  the  additional  advantage 
of  being  more  stable,  both  electrically  and  mechanically. 


2400 


2000 


1600 


1200 


soo 


400 


Distance-  Intensity  Received  Current 
on  "D/RiG/A"'wifh Pofentio"  Detector. 


In  attempting  to  improve  this  detector,  the  writer  dis- 
covered a  connection  arrangement  which  made  the  detector 
a  true  potential-operated  device.  The  other  existing  forms 
of  vacuum  detectors  as  well  as  the  many  forms  of  solid  recti- 
fiers, electrolytic,  thermal,  thermoelectric  and  other  detectors 
are  practically  all  conceded  to  be  current  operated,  and  be- 
cause of  this  fact  they  not  only  consume  energy,  but  also 


130  RADIODYNAMICS 

decrease  the  receiver's  selectivity  by  increasing  the  damping 
of  the  receiving  circuits.  This  change  in  the  receiving  circuit 
made  the  instrument  approximately  twenty-five  times  as  sensi- 
tive for  relay  or  indicating  instrument  operation;  this  can 
be  readily  observed  from  a  comparison  of  Fig.  7 1  with  Fig.  66. 
Both  curves  were  made  on  the  same  trip,  one  going  out  to 
sea  and  the  other  returning,  in  order  to  insure  the  greatest 
possible  similarity  in  the  conditions.  The  transmitting  energy 
was  also  kept  constant,  the  only  variable  factor  being  the 
distance. 

To  prove  that  this  circuit  arrangement  made  the  detector 
a  potential  operated  device,  four  of  these  detector  circuits,  each 
with  its  separate  indicating  instrument,  were  arranged  so  that 
they  could  be  simultaneously  in  connection  with  an  antenna 
circuit  tuned  to  distant  signals.  It  was  found  that  in  no  case 
was  the  signal  intensity  in  the  first  set  decreased  by  connect- 
ing on  one  or  all  of  the  other  three.  Moreover  the  signals 
in  all  four  receivers  were  approximately  equal.  The  slight 
inequalities  were  due  to  difference  in  sensitiveness  of  the 
separate  detectors.  The  effect  on  a  single  indicator  could  be 
proportionally  increased  by  connecting  it  to  the  secondary 
winding  of  a  transformer,  having  separate  primaries  which 
were  connected  to  the  separate  detectors.  Theoretically  this 
circuit  furnishes  a  means  of  securing  any  received  current 
desired,  simply  by  connecting  a  sufficient  number  of  units. 

With  these  circuits  the  vacuum  detector  can  be  adjusted  so 
that  the  paralyzing  effect  of  strong  signals  is  not  encountered. 
This  makes  the  detector  electrically  stable  and  is  a  very  im- 
portant feature.  The  detector  can  also  be  adjusted  so  that  the 
local  battery  current,  which  we  shall  call  the  field  current, 
increases  or  decreases  as  desired,  when  the  signals  arrive.  We 
will  not  attempt  to  give  a  theoretical  consideration  of  the 
detector's  action,  but  simply  explain  the  various  circuits 
employed. 


BATTLE-RANGE   TORPEDO  CONTROL 


Til 


Fig.  72  represents  a  vacuum  tube  detector,  comprising  ex- 
hausted glass  bulb  H,  in  which  are  fixed  filament  W,  grid  G, 
and  plate  F,  the  terminals  of  which  are 
T,  Ti,  T2,  and  T$.  These  terminals  lead 
through  H  in  the  usual  manner.  Fi,  Gi, 
and  Wi,  show  more  clearly  the  shapes  and 
relative  sizes  of  the  plate,  grid,  and  filament, 
respectively. 

Fig.  73  is  a  diagrammatic  representation  of 
the  author's  circuit  arrangement  for  use  with 
the  instrument  shown  in  Fig.  72.  When  used  in  a  circuit,  such 
as  that  shown  in  Fig.  72,  this  vacuum  tube  is  called  a  Poten- 
tio  detector.  That  part  of  the  diagram  included  in  the  circle 
J  is  the  Potentio  detector  circuit,  and  the  remainder  is 

simply  one  of  the  large  number 
of  ways  in  which  it  may  be  ap- 
plied in  a  radio  receiving  set. 

W  is  the  hot  wire  filament, 
which  is  maintained  at  an  in- 
candescent temperature  by  the 
battery  Bi,  the  degree  of  incan- 
descence being  varied  by  resist- 
ance R.  G  is  the  grid,  and  F 
the  plate  or  cold  electrode,  which 


FIG.  73- 


is  connected  through  the  indicating  instrument  I,  such  as  a 
telephone,  to  the  positive  pole  of  the  battery  B.  This  bat- 
tery in  practice  consists  of  about  thirty  cells;  it  is  connected 
to  W  through  the  variable  connecting  means  K.  The  grid 
terminal  T  is  connected  to  some  point  in  the  receiving  circuit 
where  the  highest  potentials  are  developed  by  the  incoming 
waves. 

In  this  receiving  circuit  A  is  the  antenna,  L  the  open  cir- 
cuit tuning  and  coupling  inductance,  C  a  variable  tuning 
condenser,  and  E  the  earth  connection.  This  open  receiving 


132 


RADIODYNAMICS 


circuit  is  coupled  to  the  closed  resonant  circuit  comprising 
inductance  Li  and  condenser  Ci. 

Fig.  74  illustrates  another  type  of  receiving  circuit  employ- 
ing the  well-known  Oudin  resonator  principle  for  increasing 
the  potentials. 

Fig.  75  illustrates  a  circuit  arrangement  and  apparatus 
used  in  producing  an  indicated  effect  greater  than  can  be 
obtained  with  one  detector.  With  ordinary  current-operated 
detectors  only  one  can  be  used  advantageously  in  a  receiv- 
ing circuit,  since  with  a  plurality  of  detectors  requiring  current 
energy  for  their  operation,  the  energy  of  the  incoming  waves  is 


LLJ 


Lz 


IU  7T 


FIG.  74. 


FIG.  75. 


divided  between  the  detectors,  and  consequently  no  increase 
in  effect  is  obtainable.  It  is  possible  and  advantageous,  how- 
ever, to  connect  a  plurality  of  Potentio  detectors  to  one 
antenna  circuit,  or  circuits  coupled  to  a  single  antenna,  in 
order  to  obtain  an  indicated  effect  much  greater  than  is 
possible  with,  one  Potentio  or  with  other  detectors. 

In  Fig.  75  the  antenna  A2,  condenser  €4,  inductance  1/3, 
and  earth  E  form  the  open  receiving  circuit.  To  a  point  of 
maximum  potential,  such  as  T5,  is  made  a  connection  which 
leads  to  the  grid  terminals  T  of  a  plurality  of  Potentio  circuits 
represented  by  0,  Oi,  and  62.  O,  Oi,  and  02  are  similar  to 
that  part  of  Fig.  73  included  in  the  line  J,  with  the  exception 


BATTLE- RANGE   TORPEDO  CONTROL 


that  the  primary  windings  P,  Pi,  and  P2  are  used  with  O, 
Oi,  and  O2  respectively  instead  of  the  indicator  represented 
by  I.  D  is  the  core  of  a  transformer  in  which  P,  Pi,  and  ?2 
are  the  primaries  acting  conjointly  on  secondary  S.  The 
latter  as  shown  is  connected  to  indicating  instrument  Ii. 
This  obviously  receives  the  effects  of  O,  Oi,  and  62  combined 
when  the  receiving  circuit  A2,  L5,  C4,  E2  is  energized  by 
received  currents. 

Fig.  76  is  the  cascade  circuit  for  amplification.     In  this  cir- 
cuit arrangement  the  received  energy  develops  potentials  in  L6 

LL|A5 


L6 


/C5" 


FIG.  76. 


FJG.  77. 


which  so  influence  the  Potentio  detector  03  as  to  cause  varia- 
tions in  the  battery  current  flowing  through  ?3.  The  varia- 
tions of  current  in  P3  induce  corresponding  variations  in  the 
secondary  winding  Si.  These  are  of  higher  potential  and  in 
turn  effect  the  induction  of  currents  of  still  higher  potential 
in  82.  The  final  effects  at  the  indicator  1 2  are  thus  increased 
considerably  over  the  initial  effects. 

Fig.  77  represents  an  adaptation  of  the  Potentio  circuit 
which  has  been  found  especially  valuable  for  the  operation 
of  indicators  of  the  galvanometer  type.  Experimental  results 
prove  it  to  give  indicated  effects  on  galvanometers  25  times 
as  great  as  those  obtainable  under  similar  conditions  with 
solid  rectifiers  and  other  well-known  detectors  of  equal 


134  RADIODYNAMICS 

sensitiveness.  No  improvement,  however,  is  noted  in  tele- 
phone operation. 

The  antenna  circuit  comprising  antenna  A4,  inductance 
coil  L8,  condenser  C6,  and  earth  £4,  is  coupled  to  the  coil  Lg 
by  means  of  L8.  The  condenser  C;  must  be  connected 
in  the  circuit  as  shown  in  order  to  secure  the  greatly  in- 
creased effect  not  noticeable  with  other  detectors  or  circuit 
arrangements. 

In  practice  63  and  Ri  are  adjusted  until  the  desired  indi- 
cation is  secured  at  13,  care  being  taken  that  the  applied 
voltage  at  63  is  not  too  high.  By  experiment  the  adjust- 
ment should  be  made  so  that  a  decrease  in  the  normal  current 
occurs  when  the  signal  arrives.  Then  by  varying  the  capacity 
of  C;  while  signal  impulses  are  arriving  the  indications  at  13 
may  be  made  to  remain  during  and  after  the  actuating  signal 
has  ceased.  The  length  of  this  time  of  indication  after  the 
signal  has  ceased  can  be  increased  or  diminished  by  variation 
of  the  capacity  Cy.  With  C;  short  circuited  or  with  the 
connection  to  C.J  broken  the  effects  at  I  are  very  much  less, 
so  that  it  can  be  readily  understood  that  the  presence  of  Cy 
between  the  cold  electrode  and  the  end  of  Lg  not  connected 
to  Gi  fulfills  the  condition  necessary  for  obtaining  the  de- 
sired operation. 

There  is  no  danger  of  burning  out  13  by  the  action  of  ex- 
cessively strong  signals,  since  with  signals  above  a  certain 
intensity  value,  the  current  in  13  will  remain  at  zero.  The 
normal  field  current  is  diminished  by  the  incoming  signals  in 
proportion  to  the  strength  of  these  signals.  This  is  another 
important  feature. 

The  Potentio  detector  stood  up  very  well  under  the  very 
severe  conditions.  It  must  be  remembered,  as  is  shown  by 
the  received  current  curve  (Fig.  71),  that  the  detector  must 
be  rugged  enough  to  remain  in  perfect  adjustment  under  the 
strongest  signals  received  within  a  few  hundred  feet  of  the 


BATTLE-RANGE   TORPEDO   CONTROL  135 

transmitter,  and  at  the  same  time  it  must  be  sensitive  enough 
to  operate  the  relay  at  the  extreme  range  of  eight  miles.  It 
must  be  capable  of  performing  these  functions  for  hours  at  a 
time,  perfectly,  without  a  single  hitch,  or  the  necessity  of 
adjustment.  The  strongest  signals  in  our  experiments  in- 
variably caused  the  familiar  "blue  arc"  between  the  plate 
and  filament,  with  the  usual  forms  of  connection  with  this 
type  of  detector.  This  necessitates  opening  and  reclosing  of 
the  field  battery  circuit  to  restore  the  normal  condition  of 
sensitiveness. 

With  the  Potentio  this  is  impossible.  The  blue  arc  is 
caused  by  too  great  a  density  in  the  ionic  field  current.  There 
is  a  critical  value  which  varies  for  different  bulbs  depending 
on  the  degree  of  exhaustion  and  the  distances  between  the 
plate  and  filament.  It  is  only  necessary  to  bring  the  field 
current  to  the  critical  value  either  by  increase  in  the  field 
battery  voltage,  or  by  superimposing  the  currents  arising 
from  incoming  signals  upon  the  normal  battery  current 
through  the  ionic  field,  to  start  the  arc, 

It  is  possible  to  obviate  this  trouble,  but  only  at  the  ex- 
pense of  sensitiveness.  The  most  sensitive  adjustment  is 
obtained  when  the  field  current  is  just  below  the  critical 
point.  If  the  incandescence  of  the  filament  or  the  voltage 
of  the  field  battery  is  reduced  sufficiently,  the  normal  field 
current  can  be  made  so  low  that  the  strongest  incoming 
oscillations  will  not  cause  a  sufficient  superimposition  of  cur- 
rent to  bring  its  value  up  to  the  critical  point.  But  the  cost 
of  this  freedom  from  arcing  is  a  great  reduction  in  sensitive- 
ness. 

The  adjustment  of  the  Potentio  is  such  that  the  normal 
field  current  is  safely  enough  below  the  critical  value  to  allow 
for  increases  due  to  occasional  vibrations  of  the  plate  and 
filament,  which  reduce  the  distance  between  them,  and  yet 
high  enough  to  insure  good  sensitiveness.  Instead  of  in- 


136  RADIODYNAMICS 

creasing  the  field  current  the  received  oscillations  decrease 
its  value.  The  strongest  signals,  instead  of  causing  the  blue 
arc,  can  only  bring  the  field  current  down  to  zero  from  its 
normal  value.  Thus  it  is  seen  that  the  signal  effect  of  the 
Potentio  is  a  change  in  the  normal  current,  —  a  change  which 
decreases  its  value  away  from  instead  of  towards  the  critical 
point;  that  instead  of  producing  excessively  strong  indicator 
operating  currents  with  excessively  strong  signals,  the 
Potentio  automatically  prevents  such  an  effect  by  ceasing  to 
furnish  an  increase  in  field  current  change  when  signals  in- 
crease above  a  certain  critical  value. 


CHAPTER  XVI 

THE  DIFFICULTIES   ENCOUNTERED    IN  PROVIDING 
PROTECTION  FROM  INTERFERENCE 

The  selectivity  problem,  which  is  by  far  the  greatest  of  all 
difficulties  to  be  overcome  i-n  the  successful  evolution  of  a  wire- 
lessly  controlled  torpedo,  is  one  of  comparative  difficulty, 
depending  upon  the  degree  of  non-interferability  desired.  A 
selective  receiver  is  like  a  safety  vault.  The  operator  at  the 
transmitter  may  be  likened  to  the  owner  of  a  safe  who  alone 
possesses  the  combination.  No  safes  are  absolutely  burglar 
proof,  and  their  value  depends  principally  on  the  length  of 
time  required  for  a  skilled  cracksman  to  reach  the  inside. 
Likewise  no  receivers  are  absolutely  selective  for  the  simple 
reason  that  an  operator  bent  on  interfering  can  take  observa- 
tions and  measurements  on  the  signals  sent  out  to  the  selec- 
tive receiver  (just  as  the  burglar  may  watch  the  opening  of 
a  safe  by  the  owner),  and  adjust  his  own  apparatus  to  emit 
waves  of  exactly  the  same  characteristics  as  those  of  the 
transmitter  designed  or  adjusted  for  the  selective  receiver's 
operation.  The  burglar,  instead  of  trying  to  learn  the  com- 
bination, may  use  sheer  force  in  reaching  the  inside  of  the 
safe.  In  the  same  manner  a  hostile  transmitting  station  can 
perform  the  desired  effect  in  the  selective  receiver,  i.e.,  operate 
the  receiving  indicator  or  relay,  by  the  emission  of  very  strong 
signals  so  that  forced  oscillations  are  set  up.  This  is  known 
as  the  "whip  crack"  effect,  and  it  is  believed  that  very  few 
receivers  are  immune  from  it. 

The  best  wireless  signaling  sets,  such  as  those  used  by  the 
U.  S.  Navy  are  considered  very  selective,  and  yet  the  inter- 


138 


RADIODYNAMICS 


ference  existent  between  them  is  very  serious.  Take,  for  ex- 
ample: Washington  (Fig.  78)  is  receiving  a  message  from  the 
Eiffel  tower  station  in  Paris,  which  is  sending  at  3000  meters 
wave  length.  It  is  easily  possible  for  a  station  in  California, 

t with    an    equal    amount    of 

power,  and  at  practically  the 
same  distance,  to  make  the 
Paris  message  unintelligible 
at  Washington,  simply  by 
sending  signals  at  or  within, 
say,  two  or  three  per  cent  of 
3000  meters  wave  length. 

Again,  some  insignificant 
station  with  little  power 
within  a  few  miles  of  Wash- 
ington, could  make  it  practi- 
cally impossible  for  them  to 
receive  any  messages  at  all 
from  distant  stations  by  send- 
ing out  broadly  tuned  sig- 
nals of  high  damping.  These 
highly  damped,  or  untuned 
signals,  by  the  previously 

mentioned  whip  crack  effect,  cause  the  receiving  antennae 
to  vibrate  in  their  own  periods,  and  thereby  produce  a  great 
deal  of  interference. 

To  illustrate:  Sing  a  clear,  steady  tone  into  a  piano.  The 
string,  which  when  struck  emits  that  tone,  will  audibly 
vibrate  in  resonance.  Then  shout  loud  and  gruffly  into  the 
same  piano;  practically  every  string  will  be  set  in  vibration, 
producing  a  dull  roar.  The  first  tone  corresponds  to  the 
signals  sent  out  by  a  tuned  transmitter;  the  second  (noise) 
to  the  whip  crack  signals  emitted  by  an  untuned  trans- 
mitter. 


FIG.  78. 

Towers  of  the  U.  S.  Naval  Station  at 
Arlington,  Va. 


PROTECTION  FROM  INTERFERENCE         139 

Another  comparison  might  serve  to  illustrate  the  degree  of 
selectivity  necessary  for  torpedo  control.  We  have  three 
persons  A,  B,  and  C.  A  and  B  are  together  at  one  place,  and 
C  is,  say,  a  mile  away.  The  problem  is  to  allow  A  to  hear 
what  C  says  while  B  is  shouting  in  his  ear.  Impossible,  you 
say?  Yet  the  torpedo  problem  is  practically  an  exact  analogy. 
We  must  be  able  to  make  the  electromagnetic  ear  of  the 
torpedo  hear  our  control  impulses  eight  miles  away  while  it 


FIG.  79. 
Transmitter  of  Telefunken  5  kw.  set  aboard  U.  S.  S.  South  Carolina. 

is  at  the  very  side  of  a  battleship  capable  of  almost  deafening 
it  with  the  force  of  it's  own  powerful  signals. 

It  is  true  that  we  could  sidetrack  the  real  problem,  and 
simply  use  such  a  large  amount  of  energy  at  our  shore  station, 
that  more  energy  could  be  delivered  to  the  torpedo  at  eight 
miles  than  the  hostile  battleship  could  deliver  at  a  hundred 
feet.  This  is  possible  because  the  amount  of  energy  that  can  be 
efficiently  used  aboard  a  modern  battleship  does  not  greatly 
exceed  5  kw.  Such  a  5  kw.  set  is  shown  in  Figs.  79  and  80. 
This  is  due  to  the  limited  size  of  the  antenna.  A  shore  station, 
with  practically  no  limits  on  the  size  and  height  of  its  antenna, 


140 


RADIODYNAMICS 


can  easily  use  100  kw.  The  shore  station  also  has  the  advan- 
tage of  being  able  to  direct  its  energy  somewhat  in  the  general 
direction  of  operations.  This  can  be  accomplished  either  by 
the  use  of  an  inverted  L-type  antenna,  with  a  flat  top  long  in 
proportion  to  its  height,  as  suggested  by  Marconi,  or  by 
means  of  the  Bellini-Tosi  Radiogoniometer. 


FIG.  80. 
Receiving  set  aboard  U.  S.  S.  South  Carolina. 

Sidetracking  the  real  problem  by  using  a  land  station  of 
tremendous  power  is,  however,  not  the  practical  and  efficient 
solution.  In  the  first  place,  although  desirable,  absolute 
selectivity  is  not  necessary.  A  receiver  that  will  require,  say, 
fifteen  minutes  time  for  the  enemy  to  learn  its  combination, 
will,  in  all  probablity,  satisfy  the  requirements. 

We  have  described  the  systems  used  by  the  principal  in- 
vestigators abroad;  those  who  have  observed  closely  will 
have  seen  at  once  that  not  one  of  these  systems  is  immune  to 
intentional  interference  for  the  simple  reason  that  no  pro- 
vision is  made  for  avoiding  the  broadly  tuned  or  whipcrack 
signals,  that  may  be  sent  out  by  any  transmitter. 


PROTECTION  FROM  INTERFERENCE         141 

What  use,  we  may  then  ask,  and  well,  are  the  various  types 
of  codal  selectors  and  protective  devices,  when  any  hostile 
battleship  can  absolutely  lock  the  receiving  apparatus  so 
that  not  even  the  controlling  operator  can  get  in  a  signal, 
by  the  simple  process  known  to  operators  as  "  sitting  on  the 
key." 

Systems  like  those  of  Anders  Bull,  Walter,  Branley,  and 
others,  providing  complicated  apparatus,  aside  from  not  being 
able  to  cope  with  interference,  actually  defeat  their  own  end 
by  their  very  presence;  designed  to  increase  the  reliability  of 
operation,  they  diminish  it  by  increasing  the  number  of 
mechanisms,  especially  those  electrically  operated,  which  are 
likely  to  get  out  of  order. 

The  keynote  of  success  in  developing  mechanisms  that  must 
operate  without  adjustment  is  simplicity.  The  simplest  form 
of  distributor  that  will  accomplish  the  end  in  view,  namely, 
to  close  any  one  of  a  number  of  circuits,  is  all  that  is  neces- 
sary and  indeed  is  to  be  greatly  preferred.  Wirth's  ap- 
paratus which  provides  means  of  changing  the  receiver's 
wave  length,  is  somewhat  nearer  the  solution,  but  it,  like 
the  others,  provides  no  means  of  getting  away  from  forced 
oscillation  effects;  any  system  that  does  not  do  this  is  useless 
for  torpedo  control. 

The  selectivity  problem  cannot  be  solved  by  any  form  of 
codal  selector  or  protective  device  inserted  in  the  receiving 
circuits  after  the  relay;  they  must  be  placed  before  the  relay, 
that  is,  they  must  protect  it  from  interference  if  they  are  to 
serve  their  purpose.  Instruments  like  the  resonance  relays 
and  monotelephone  amplifiers  have  this  protection  inherently 
by  virtue  of  their  vibratory  elements  tuned  to  the  spark 
frequency  of  the  transmitter,  but  these,  as  pointed  out  else- 
where, are  subject  to  vibration,  shocks,  and  sounds. 

In  order  to  reach  the  solution  we  must  devise  systems  that 
not  only  have  a  high  degree  of  selectivity  for  tuned  signals, 


142  RADIODYNAMICS 

but  also  provide  means  of  evading  the  whip  crack  effects  of 
broadly  tuned  or  plain-aerial  transmitters. 

Interference  preventers  have  been  invented,  which,  to  a 
large  extent,  prevent  disturbances  from  untuned  transmitters 
of  whip  crack  signals.  At  Washington,  in  1910,  the  writer 
witnessed  government  tests  of  such  a  receiver,  worked  out  by 
Fessenden.  Reception  of  signals  from 
a  station  about  400  miles  away,  at 
Brant  Rock,  Mass.,  was  carried  on 
while  a  five-kilowatt  station  less  than 
a  mile  away  was  sending  interfering 
signals.  The  wave  lengths  of  the  two 
transmitters  were  different  by  only  a 
few  per  cent.  Fig.  81  is  a  diagram  of 
JLW  this  receiver.  The  relation  between 
the  two  sets  of  coils  is  such  that  when 
the  same  current  passes  through  the 
E  two  primaries,  no  current  is  induced 

FlG "  gi  in    the    secondary   circuit,    the    two 

secondary  inductances,  Li    and    L2 

being  wound  in  opposition.  By  tuning  each  circuit  separately 
to  the  incoming  signals,  and  then  throwing  one  of  them  slightly 
out  of  tune,  the  broadly  tuned  and  whip  crack  signals  will 
divide  equally  between  the  two  primaries,  while  the  tuned 
signals  will  be  received  by  one  side  alone,  their  strength  un- 
diminished  by  the  presence  of  the  other  circuit  to  ground. 

When  such  a  receiver  is  used  in  conjunction  with  a  trans- 
mitter of  the  undamped,  continuous  wave  type,  like  the  high 
frequency  alternator,  or  the  Duddell-Thompson  arc,  a  very 
considerable  degree  of  freedom  from  interference  is  possible 
for  acoustic  signaling. 

Whether  such  a  system  is  selective  enough  for  torpedo 
control  depends  upon  the  effectiveness  of  two  possible  methods 
of  producing  interference.  One  is,  to  listen  for  the  controlling 


PROTECTION  FROM  INTERFERENCE  143 

impulses,  measure  their  wave  length,  and  then  adjust  their 
own  transmitter  to  send  out  similar  signals.  Whether  or  not 
they  can  do  this  in  the  time  necessary  for  the  torpedo  to  reach 
them  (probably  ten  minutes),  is  not  known.  Since  probably 
not  more  than  twenty-five  short  course-correcting  impulses  are 
necessary  to  guide  the  torpedo  to  a  target  to  a  distance  of,  say, 
six  miles^  it  is  a  matter  of  conjecture.  The  other  interference 
method  is  to  use  one  of  the  siren  interference  machines  in- 
vented in  Germany.  It  consists  essentially  of  a  set  of  rotat- 
ing switches,  which  automatically,  and  in  rapid  succession, 
cause  a  series  of  sharply  tuned  waves  of  gradually  increasing 
length  to  be  emitted.  This,  however,  as  an  interference  de- 
vice, has  the  disadvantage  that  the  available  power  is  divided 
among  the  different  wave  lengths  used. 

Assume  that  the  energy  is  5  kw.,  and  that  we  use  20  sepa- 
rate wave  lengths.  The  energy  on  each  wave  length  (not 
taking  into  consideration  the  difference  in  efficiency  with 
change  in  wave  length)  is  one-twentieth  of  the  total  or  one- 
fourth  kilowatt.  For  telephone  operation  this  would  not 
apply,  since  that  instrument  would  give  the  full  indication 
during  the  short  time  that  the  particular  wave  length  affect- 
ing it  was  being  emitted,  and  thus  make  reception  of  other 
signals  impossible;  but  for  relay  operation  unless  the  separate 
wave  lengths  were  each  emitted  for  a  time  equal  to  the  me- 
chanical vibration  period  of  the  relay's  movable  element,  or 
longer,  the  effect  would  be  equivalent  to  the  effect  of  a  one- 
fourth  kilowatt  transmitter  in  continuous  operation  on  the 
correct  wave  length.  Even  though  the  rotating  switches 
were  rotated  at  a  speed  slow  enough  to  cause  a  closure  of  the 
relay  each  time  the  correct  wave  length  was  emitted,  the 
fact  that  nineteen  other  similar  wave  lengths  must  be  sent 
out  in  succession,  each  for  the  same  length  of  time,  makes 
the  interfering  impulses  so  far  between  that  corrections  can 
be  made  from  the  control  station. 


144  RADIODYNAMICS 

The  second  method,  even  with  the  limitations  explained, 
is  probably  the  better  of  the  two  methods,  as  the  shore  station 
could  send  out  confusing  or  blind  signals  differing  in  wave 
length  from  the  steering  impulses,  so  that  the  enemy  afloat 
would  have  no  means  of  determining  which  was  actually  the 
correct  one. 

In  order  to  increase  the  selectivity  of  torpedo  operation  to 
such  a  point  where  interference  is  much  more  impractical, 
Mr.  Hammond  and  the  writer  worked  out  a  number  of  Selec- 
tive control  systems.  Of  these  only  a  few  will  be  described. 
Since  the  work  done  along  this  line  at  the  Hammond  Radio 
Research  Laboratory  is  practically  the  only  work  of  this 
kind  in  the  United  States,  and  since  nothing  new  is  forthcom- 
ing from  European  inventors,  these  selective  systems  repre- 
sent the  latest  improvement  along  this  line. 


CHAPTER  XVII 


A  MEANS   OF  OBTAINING  SELECTIVITY 

Selective  Transmitter-Receiver  Unit.  —  Fig.  82  illustrates  a 
type  of  transmitter-receiver  unit  suggested  by  the  writer  in 
1911.  H.F.A.  is  a  high-frequency  alternator,  or  other  high- 
frequency  current  producer,  which  supplies  energy  to  Li 
through  interrupters  Ii,  12,  and  key  K. 

The  principle  applied  in  this  selectivity  scheme  is  the  same 
as  that  brought  forward  by  Blondel  in  his  spark-tuned  re- 

41    ^ 

Ai  Az 


H.F, 


L3  I 


FIG.  82. 

ceiver  some  time  ago,  but  it  has  the  additional  selectivity  of 
one  or  more  other  circuits,  besides  the  high-frequency  and 
spark-tuned  circuits.  Moreover,  this  other  circuit,  which  is 
tuned  to  an  intermediate  frequency  between  the  two  men- 
tioned at  the  transmitter,  has  an  inaudible  periodicity,  so 
that  the  signals  cannot  be  heard  at  all  by  an  ordinary  re- 
ceiver. The  wave  length  of  this  inaudible  frequency  is  so 
far  above  the  wave  lengths  used  in  signaling  that  the  ordi- 
nary receiving  circuits  will  not  respond  to  it,  and  so  far  below 
that  of  the  spark-tuned  circuits  that  they  would  give  no  indi- 
cation even  if  the  frequency  were  audible. 

145 


146 


RADIODYNAMICS 


Supposing  the  stiffness  of  the  receiving  circuits  is  such  as 
to  require  twenty  impressed  oscillations  to  swing  them  up  to 
full  amplitude,  then  the  ratio  of  the  different  frequencies  at 
the  transmitter  should  be  20  to  i,  that  is,  the  transmitter 
emits  several  frequencies,  all  in  the  same  wave,  the  values 
of  which  drop  down  in  steps  according  to  the  ratio  20  to  i  or 
the  ratio  found  most  suitable. 

Consider  the  wave  length  of  the  emitted  waves  to  be  1000 
meters.  The  oscillation  frequency  corresponding  to  that 
value  is  300,000  per  second.  The  oscillation  frequency  at 
H.F.A.  would  then  be  300,000.  Allowing  20  oscillations  to 

141 


L35 


D.C. 


FIG.  83. 


FIG.  84. 


the  wave  train,  the  interrupter  Ii  would  have  a. frequency  of 
15,000  per  second.  That  is,  at  each  contact  of  Ii,  20  com- 
plete oscillations  from  H.F.A.  would  occur  in  Li  and  be 
radiated  from  A.  Dividing  15,000  by  20  we  have  750,  the 
frequency  of  interrupter  12.  When  key  K  is  closed  antenna 
A  then  radiates  electric  waves  of  1000  meters  length,  which 
are  broken  up  into  an  inaudible  group  frequency  by  Ii.  This 
resultant  signal  is  then  broken  up  into  a  frequency  of  a  lower 
order,  determined  by  the  speed  of  12. 

Figs.  83  and  84  show  two  other  ways  of  obtaining  the  same 
results  as  with  Fig.  82.  In  Fig.  83  G  is  an  alternating-current 
generator  having  a  periodicity  of  about  7500  cycles,  which 
excites  the  field  windings  of  high-frequency  alternator  H.F.A., 


A   MEANS  OF  OBTAINING  SELECTIVITY  147 

the  latter  being  rotated  at  such,  speed  as  to  give  a  300,000- 
cycle  current.  The  current  delivered  by  H.F.A.  will  then 
have  a  periodic  amplitude  variation  of  a  frequency  correspond- 
ing to  G,  namely  15,000.  H.F.A.  delivers  this  periodically 
varying  3oo,ooo-cycle  current  through  interrupter  I  and  key 
K,  to  antenna  A  by  means  of  the  inductively  coupled  coils, 
Li  and  L2. 

When  interrupter  I  is  stationary  or  short  circuited,  an- 
tenna A  radiates  electric  waves  of  1000  meters  length  at  an 
amplitude  frequency  of  15,000,  which  being  above  the  audible 
limit,  will  not  be  heard  by  a  spark  receiving  set.  If  I  is 
rotating  so  as  to  give  750  contacts  per  second,  A  will  radiate 
this  wave  of  two  periodic  characteristics  at  a  rate  of  750  per 
second,  which  of  course  is  audible.  Thus  in  Fig.  83  G  takes 
the  place  of  Ii,  in  Fig.  82,  for  producing  the  15,000  per  second 
group  frequency. 

Fig.  84  shows  another  method  of  producing  a  high-fre- 
quency current  having  two  or  more  group  frequencies  within 
or  out  of  the  range  of  audibility.  B  is  an  arc  oscillatory-cur- 
rent generator  of  the  Duddell-Thompson  type,  fed  from  a 
source  of  direct  current.  In  shunt  around  the  arc  is  a  con- 
denser, Ci,  inductance,  L2,  and  interrupter,  I. 

Consider  I  as  being  short  circuited  and  circuit  B-C-Li 
open,  then  as  is  well  known  in  the  art,  when  B,  Ci,  and  L2 
are  properly  adjusted,  oscillatory  currents  will  be  generated 
in  the  circuit  B-Ci-L2,  the  frequency  of  the  alternating 
currents  developed  being  dependent  principally  on  the  values 
of  Ci  and  L2.  Now  if  circuit  B-C-Li  be  closed  oscillations 
will  be  generated  in  it  of,  say,  7500  cycles.  This  has  the 
effect  of  producing  a  7500  cycle  amplitude  variation  of  the 
current  of  the  circuit  B-Ci-L2  and  antenna  A  being  in 
resonance  with  B-Ci-L2,  will  radiate  electric  waves  of 
300,000  oscillatory  frequency,  and  at  a  group  frequency  of 
15,000  impulses  per  second. 


148 


RADIODYNAMICS 


Now  if  interrupter  I,  giving  750  contacts  per  second,  be 
included  in  the  circuit  B-Ci-L2,  the  radiated  waves  will  be 
broken  up  into  the  audible  frequency  of  750  per  second. 

The  receiving  circuits,  as  shown  in  Fig.  82,  are  tuned  to  the 
oscillatory  current  frequency,  the  inaudible  amplitude  fre- 
quency, and  the  audible  group  frequency.  Antenna  circuit 
A2-L3-C  and  circuit  L4~Ci  are  both  tuned  to  the  trans- 
mitter oscillation  frequency.  By  the  action  of  rectifier  Ri, 
L5  receives  unidirectional  currents  from  L4~Ci,  thereby 
energizing  circuit  L6-L7-C2,  which  is  in  resonance  with  the 
frequency  produced  by  the  interrupter  giving  15,000  contacts 

*UJ 


FIG.  85, 


FIG.  86. 


per  second.  If  12  of  Fig.  82  is  in  operation,  circuit  L8-C3-P 
will  then  be  energized,  and  telegraphic  signals  may  be  pro- 
duced at  P  by  the  transmitting  key  K. 

Figs.  85  and  86  show  two  other  methods  of  producing  the 
ultra  audible  group  frequencies  of  the  high-frequency  currents. 
In  Fig.  85,  I  is  a  high-frequency  alternator  supplying  current 
to  antenna  6  through  interrupter  3  and  key  2,  and  coupling 
coils  4  and  5.  Motor  7  is  mechanically  connected  to  coil  5 
and  rotates  it  in  such  a  way  as  to  produce  a  periodic  ampli- 
tude variation,  the  frequency  of  which  is  ultra-audible. 

In  Fig.  86,  antenna  8  is  inductively  connected  to  high- 
frequency  alternator  12  and  ultra-audible  frequency  alter- 


A   MEANS  OF  OBTAINING  SELECTIVITY  149 

nator  16  by  means  of  coupling  coils  9  and  10,  and  14  and  15 
respectively.  An  interrupter  n  and  key  13  are  in  circuit 
with  12. 

When  the  transmitter  is  in  operation,  n  interrupts  the 
current  from  12  at  an  audible  rate,  and  by  the  action  of  16, 
the  amplitude  of  the  antenna  current  is  varied  periodically, 
the  periodicity  being  dependent  upon  the  frequency  of  16. 


CHAPTER   XVIII 

NATURE   OF  INDICATOR   CURRENTS   IN  RADIO 
RECEIVERS 

The  absolute  necessity  for  a  simple  and  effective  inter- 
ference preventer  for  our  torpedo  control  system  led  the 
author,  in  the  fall  of  1912,  to  investigate  the  nature  of  the 
phenomenon  accompanying  the  reception  and  indication  of 
alternating-current  waves  of  radio  lengths. 

Prof.   G.  W.  Pierce,  of  Harvard  University,  has  already 
done  considerable  work  along  this  line,  and  in  his  book  on 
I  I        the  "  Principles  of  Wireless  Telegraphy  "  are  found  the 
results  of  his  extensive  researches  on  detectors  and 
rectification    phenomena,   together    with   hypotheses 
:  r~l  based  on  them.     Although  Professor  Pierce's  work  has 
been  mainly  along  the  line  of  determining  the  cause  of 
rectification  in  radio  detectors,  he  also  presents  brief 

but  concise  discussions  on  the  nature  of  the  received 
FIG.  87. 

currents  in  the  indicator  circuit. 

On  pages  173-174,  explaining  the  action  of  solid  rectifiers 
in  a  receiving  circuit  like  that  shown  in  Fig.  87,  he  says: 

"A  train  of  incoming  waves  produces  an  alternating  e.m.f. 
in  the  antenna  circuit.  This  e.m.f.,  when  in  one  direction, 
produces  a  large  current  through  the  detector,  charging  the 
antenna.  When  the  e.m.f.  reverses  the  current  from  the 
antenna  to  the  ground  through  the  carborundum  is  smaller, 
thus  leaving  the  antenna  charged  with  a  small  quantity  of 
electricity.  The  effect  of  the  whole  train  of  waves  is  addi- 
tive, so  that  this  charge  on  the  antenna  is  cumulative.  The 
accumulated  charge  on  the  antenna  escapes  through  the 


NATURE  OF  INDICATOR  CURRENTS  151 

telephone  shunted  about  the  carborundum,  causing  the  dia- 
phragm to  move.  Each  subsequent  train  of  waves  causes  a 
similar  motion  of  the  diaphragm,  which  is  evidenced  as  a  note 
in  the  telephone,  equal  in  pitch  with  the  train  frequency  of 
the  waves. 

"It  is  immaterial  whether  the  detector  permits  the  larger 
current  to  flow  upward,  charging  the  antenna  positively,  or 
permits  the  larger  current  to  flow  in  the  downward  direction, 
charging  the  antenna  negatively.  The  explanation  is  the 
same  in  both  cases. 

"With  very  slight  change  this  explanation  can  be  made  to 
apply  also  to  those  cases  in  which  the  detector  is  in  a  con- 
denser circuit  coupled  inductively  or  directly  with  the  antenna 
circuit." 

Such  a  modification  consists  essentially  in  substituting  the 
stopping  condenser  for  the  capacity,  and  the  coupling  coil 
for  the  inductance  of  the  antenna.     That  the  two 
circuits  are  of  the  same  type  is  seen  by  an  inspec- 
tion of  Figs.  87  and  88.     In  both  cases  the  detector      .      ,. 
has  the  alternating  e.m.f .  impressed  upon  it  and,     1 1      • 
as  Dr.  Pierce    told    the    author   personally,  the 
charge  accumulates,  in  the  stopping  condenser, 
and  discharges  through  the  indicator  at  a  rate      FlQ  88 
equal  to  the  transmitter's  group  frequency,  and 
in  exactly  the  same  manner  as  in  the  previously  mentioned 
circuit. 

The  best  value  for  the  stopping  capacity,  if  this  be  true, 
would  be  such  that  with  signals  of  medium  intensity,  it  would 
be  completely  charged  by  one  wave  train.  The  resistance  of 
the  receiving  telephone  also  influences  their  best  value,  and 
must  be  taken  into  consideration. 

The  application  of  such  an  explanation  to  relay  operation 
is,  however,  of  principal  interest  to  us.  There  is  no  reason 
why  the  theory  applied  to  arriving  wave  trains  of  1000  per 


152  RADIODYNAMICS 

second  frequency  should  not  hold  equally  well  for  trains  of 
much  greater  length,  provided  the  stopping  condenser  is 
large  enough  to  absorb  all  the  energy  delivered  by  the  rectifier 
during  that  longer  train.  Neither  is  there  any  reason  ap- 
parent why  wave  trains  composed  of  equal  amplitude  oscilla- 
tions should  not  act  in  the  same  way  as  do  the  damped  trains. 

Granting  these  suppositions,  we  could  use  undamped  oscil- 
lations in  trains  of  any  length,  and  a  stopping  condenser 
sufficiently  large  to  absorb  all  the  energy  supplied  to  it  during 
that  time  by  the  detector.  At  the  end  of  the  wave  train  then 
the  accumulated  charge  in  the  condenser  would  discharge 
through  the  relay  with  much  greater  effect  than  could  be 
obtained  with  short  successive  wave  trains.  Experiments 
based  on  these  suppositions  were  performed,  but  no  increased 
relay  deflections  could  be  obtained. 

In  a  sketch  of  the  action  of  wireless  telephonic  apparatus, 
on  page  305  of  his  book,  Dr.  Pierce  says: 

"The  receiving  apparatus  is  identical  with  that  employed 
in  wireless  telegraphy,  and  makes  use  of  a  receiving  antenna 
coupled  with  a  circuit  containing  some  type  of  rectifying 
detector;  e.g.,  an  electrolytic  detector,  a  crystal  contact  de- 
tector, or  a  vacuum  tube  rectifier.  About  the  detector  is 
shunted  a  sensitive  telephone  receiver. 

"The  action  is  as  follows:  If  an  unmodified  train  of  electric 
waves  having  a  frequency  higher  than  the  limit  of  human 
audibility  (35,000  vibrations  per  second)  arrives  at  the  re- 
ceiving station,  the  receiving  circuit,  if  properly  tuned,  will 
sustain  electric  oscillations  which,  passing  through  the  de- 
tector, will  be  rectified  and  will  give  a  series  of  rectified  im- 
pulses to  the  receiving  telephone  circuit. 

"These  impulses,  being  all  in  one  direction,  will  act  as  a 
continuous  pull  on  the  diaphragm,  —  a  continuous  pull  for 
the  reason  that  the  diaphragm  cannot  follow  the  rapid  suc- 
cessive impulses,  and  because  also,  on  account  of  the  inductance 


NATURE  OF  INDICATOR   CURRENTS  153 

of  the  telephone  circuit  these  impulses  are  modified  electrically 
into  practically  continuous  current  through  the  receiver.''' 

An  application  of  this  explanation  for  a  receiver  which 
discriminates  between  spark  and  undamped  wave  signals 
for  relay  operation  at  once  suggests  itself.  If  the  inductance 
of  the  telephone  or  relay  is  high  enough  to  smooth  the  high- 
frequency  direct-current  impulses  into  a  practically  con- 
tinuous current,  the  indicator  current,  then,  with  unbroken, 
undamped  oscillations,  is  practically  unvarying  and  uni- 
directional. For  spark  signals  or  chopped  continuous  wave 
signals  of  audible  frequencies,  the  high-frequency  direct- 
current  impulses  are  modified  into  one  impulse  the  length  of 
the  train,  but  the  self -inductance  of  the  indicator  is  insufficient 
to  appreciably  affect  these  longer  train-length  impulses,  so 
that  they  pass  through  unmodified.  However,  by  inserting 
a  choke  coil  of  large  value,  the  broken  signals  may  be  greatly 
reduced  in  intensity,  while  the  unbroken  signals  remain 
practically  the  same  as  before,  except  for  a  decrease  in  ampli- 
tude due  to  the  added  ohmic  resistance  of  the  choke  coil.  A 
selective  receiver  based  on  this  principle  will  be  described  in 
a  subsequent  chapter. 

That  these  two  explanations  do  not  agree  is  evident,  but 
it  is  difficult  to  understand  why  the  action  for  continuous 
waves  should  be  other  than  the  action  for  damped  trains  of 
waves. 

In  November  of  1912  the  writer  performed  some  experi- 
ments in  the  effort  to  verify  either  of  Pierce's  theories,  or  to 
unearth  the  true  explanation  of  the  nature  of  the  received 
current  in  the  indicator  circuit.  These  experiments,  although 
crude  and  incomplete  seem  to  shed  new  light  upon  this  little 
investigated  phenomenon. 

The  writer  presents  the  data  and  conclusions  derived  from 
these  tests  in  the  hope  that  they  may  incite  further  investi- 
gation. 


RADIODYNAMICS 


Experimental  Determination  of  the  Nature  of  the  Indicator- 
operating  Currents  in  a  Radio  Receiver 

Fig.  89  shows  diagrammatically  the  connections  and 
arrangement  of  apparatus,  and  the  following  table  gives  data 
relative  to  the  apparatus  used. 


FIG.  89. 

B Storage  battery. 

E Ericcson  test  buzzer. 

K Key. 

V Murdock  variable  condenser  (max.  cap.  0.002  mfd.)  set  at  100° 

Vi Murdock  variable  condenser  (max.  cap.  0.002  mfd.)  set  at  120° 

V2 Murdock  variable  condenser  (max.  cap.  0.002  mfd.)  set  at  45° 

V3 Murdock  variable  condenser  (max.  cap.  0.002  mfd.)  set  at  60° 

¥4 Murdock  variable  condenser  (max.  cap.  0.002  mfd.)  set  at  180° 

P Primary  Murdock  inductive  tuner  69  turns. 

Pi Primary  Murdock  inductive  tuner  72  turns. 

S Secondary  Murdock  inductive  tuner,  contact  stud  No.  2. 

Si Secondary  Murdock  inductive  tuner,  contact  stud  No.  3. 

D Iron  pyrite  detector. 

Di Iron  pyrite  detector. 

F 3ooo-ohm  Schmidt- Wilkes  telephone  receiver. 

R Weston  relay  (microammeter  movement). 

Fi 300-ohm  Marconi  wavemeter  phone. 

L 2500-ohm,  8-c.  p.,  carbon  filament  lamp.  ' 

1 25oo-ohm  (d.  c.)  No.  34  copper  wire  coils  (2)  on  a  laminated  wire 

core. 
H Distance  of  apparatus  in  circle  from  remainder,  10  feet. 

Experiments  and  Observations 

With  the  apparatus  arranged  and  adjusted  as  shown  and 
in  operation,  the  following  experiments  and  observations  were 
made: 


NATURE  OF  INDICATOR  CURRENTS  155 

1.  Test  for  tuning:  With  the  coupling  between  the  coils  of 
the  two  tuners  moderately  weak  (secondaries  about  three- 
fourths  the  way  out  of  primaries),   the   tuning  was  fairly 
sharp,  the  point  of  maximum  signal  intensity  being  capable 
of  determination  to  within  i  or  2  degrees  on  either  of  the 
variable  tuning  condensers,  V,  Vi,  or  ¥3. 

2.  To  prove  that  tertiary  circuit,  Si-V3,  does  not  receive 
its  energy  direct  from  primary  exciting  circuit,  V-P,  instead 
of  from  the  rectifier  D,  as  intended:    Signals  in  F  were  di- 
minished to  inaudibility  by  variation  of  Vi. 

3.  Test  for  difference  in  energy  between  secondary  (S-Vi), 
and  tertiary  (Si-V3)  circuits:    F  connected  across  D,  with 
Pi  disconnected,  indicated  a  signal  that  was  only  slightly 
greater  than  at  Di. 

4.  With  D  elements  out  of  contact,  it  was  found  necessary 
to  change  Vi  to  60  degrees  for  resonance,  but  signals  at  F 
were  very  sharply  tuned  and  much  stronger. 

5.  R,  Fi,  L,  and  I  were  separately  thrown  in  circuit  with 
D  and  Pi  with  the  following  results  at  F,  the  signal  inten- 
sities being  in  the  order  given. 


i O. 

2 R. 

3 ....Fi 


No    great  difference  between    the  intensities; 
signals  moderately  strong. 

4 L. 

5 1.       Signals  very  weak. 

6.  All  apparatus  included  by  circle  H  was  replaced  by  a 
closely  coupled  set  of  coils  on  a  laminated  core,  a  variable 
condenser,  and  a  telephone,  all  compris- 
ing a  low-frequency  oscillatory  circuit  of 
such  wave  length  as  to  respond  to  the 
group  frequency  of  the  buzzer  signals. 
(See  Fig.  90.)  The  signals  at  F2  were  considerably  reduced 
with  this  arrangement,  but  fairly  good  spark  tuning  could  be 
secured. 


156  RADIODYNAMICS 

7.  Change  of  detectors  at  D:  Detectors  of  various  types, 
such  as  the  different  forms  of  the  vacuum  tube  rectifier, 
carborundum,  and  electrolytic,  were  used  at  D  with  practi- 
cally no  change  in  results,  save  that  in  some  instances  the 
signals  through  the  whole  series  of  tests  were  stronger  or 
weaker  due  to  differences  in  detector  sensitiveness. 

Conclusions  Drawn  from  Tests 

The  very  fact  that  energy  in  the  form  of  tuned  high-fre- 
quency oscillatory  currents  is  developed  in  the  tertiary 
circuit  is  a  proof  that  the  effect  of  a  train  of  waves  is  not  ad- 
ditive; that  the  whole  train  of  waves  does  not  pass  through 
the  indicator  as  a  single  pulse  in  one  direction,  but  that  each 
separate  impulse  in  the  train  passes  through  the  indicator 
without  losing  its  distinctness,  and  is  not  smoothed  down  into 
one  impulse  with  the  others  in  the  train.  The  fact  that  this 
tertiary  circuit  was  10  feet  distant  from  the  other  circuits, 
and  the  fact  that  when  the  audions  were  used  as  detectors, 
the  signals  at  F  could  be  cut  out  completely  by  de-energizing 
the  filament,  show  conclusively  that  the  currents  in  the 
tertiary  circuit  were  not  set  up  by  direct  induction  from  the 
primary  exciting  circuit,  and  that  therefore  they  were  due  to 
the  "blow  excitation"  of  the  distinct  high-frequency  direct- 
current  impulses  arriving  from  D,  the  rectifier.  The  fact 
that  there  was  tuning,  and  that  the  selectivity  was  so  good 
that  the  signals  at  F  could  be  rendered  inaudible  by  varia- 
tion of  Vi,  also  strongly  .support  this  proof. 

The  fact  that  the  signals  at  F  were  very  nearly  as  strong 
as  when  F  was  connected  across  D,  indicates  that  the  rectified 
high-frequency  impulses  were  not  flattened  greatly,  due  to 
inductive  resistance,  as  otherwise  the  energy  delivered  by 
Di  to  F  could  not  have  been  so  great,  and  the  tuning  would 
not  have  been  so  good. 

With  D  out  of  contact  the  result  was  simply  to  connect  V2 


NATURE  OF  INDICATOR  CURRENTS  157 

in  parallel  with  Vi,  Pi  being  in  this  connecting  line,  the  wave 
length  being  thereby  increased  so  that  it,  was  necessary  to 
decrease  Vi  to  60  degrees  in  order  to  restore  resonance  con- 
ditions; the  current  in  Pi  was  therefore  alternating  instead 
of  pulsating  direct,  and  maximum  value  instead  of  half  value, 
due  to  the  chopping  off  action  of  the  rectifier.  The  signals 
at  F  were,  therefore,  much  stronger. 

The  fact  that  there  was  no  very  noticeable  decrease  in 
signal  intensity  when  N  was  changed  successively  from  O  to 
R,  F,  and  L,  apparently  indicates  two  things,  namely:  (i)  the 
resistance  of  the  detector  D  was  very  high,  for  additional 
resistances  up  to  2500  ohms  in  its  circuit  with  P  did  not 
greatly  change  the  total  resistance  of  the  circuit,  since  by 
their  addition  the  signals  were  not  greatly  diminished;  and 
(2),  coils  of  wire  wound  on  magnetized  or  permanent  magnet 
cores  present  little  inductive  resistance  to  high-frequency 
pulsating  currents.  (The  coil  of  the  Weston  relay  R  sur- 
rounds a  core  magnetized  by  the  permanent  magnet  of  the 
instrument;  the  coils  of  the  Marconi  phone,  Fi,  are  wound 
on  permanent  magnet  poles.) 

When  I,  the  coils  of  copper  wire  inductively  wound  on  a 
laminated  core,  having  a  resistance  equal  to  that  of  the  lamp, 
L,  was  connected,  the  signals  became  very  nearly  inaudible. 
This  shows  that  inductances  with  soft,  laminated  iron  cores 
present  a  relatively  high  inductive  resistance  to  high-frequency 
pulsating  currents.  Since  these  coils  had  considerable  dis- 
tributed capacity  it  is  believed  the  weak  signals  that  were 
heard  were  due  to  the  conductive  effects  of  this  capacity. 

The  intensity  of  the  signals  was  decreased  to  this  great 
extent,  because  the  high-inductive  resistance  of  I  obliterated 
the  separate  pulses  in  the  train,  and  lumped  them  into  one 
unidirectional-current  impulse  the  length  of  the  train,  which, 
having  a  very  low  frequency,  could  not  swing  up  circuit 
Si-V  into  resonant  operation;  the  detector  Di  and  tele- 


158  RADIODYNAMICS 

phone  F,  therefore  received  no  energy,  and  so  no  signals  were 
heard. 

That  this  lumping  action  does  occur  was  shown  with 
the  low-frequency  tuned  circuit,  which  responded  to  the 
group  frequency  of  these  impulses.  The  reduction  in  in- 
tensity of  the  received  current  at  F2  in  this  low-frequency 
circuit  was  due  to  the  fact  that  with  the  apparatus  at  hand, 
a  high  resistance  was  inevitable  in  order  to  secure  the  in- 
ductance necessary  for  obtaining  the  long  wave  length  re- 
quired in  that  circuit. 

The  tests  with  different  detectors  show  that  all  give  prac- 
tically the  same  effects. 


CHAPTER   XIX 
THE  INTERFERENCE   PREVENTER 

The  writer  devised  this  receiver  in  order  to  utilize  fun- 
damental principles  relating  to  the  flow  of  direct  and 
alternating  currents  for  the  production  of  a  highly  selective 
radio  system. 

These  properties  have  been  applied  in  wire  telephony,  and 
kindred  branches  of  the  electrical  arts,  and,  more  specifically, 
deal  with  electrical  circuits  and  their  properties.  These 
properties  may  be  so  varied  as  to  make  the  circuit  conductive 
to  currents  of  constant  value,  while  greatly  resisting  the  flow 
of  varying  currents,  and  vice  versa.  In  other  words,  by  in- 
serting an  electrostatic  condenser  in  a  metallic  circuit  con- 
nected to  a  source  of  alternating  potentials,  an  alternating 
current  would  flow,  but  the  same  circuit  would  present  an 
infinitely  high  resistance  to  the  flow  of  a  direct  current. 
Also  by  inserting  a  coil  of  high  self-inductance  in  a  metallic 
circuit  connected  to  a  source  of  direct  unvarying  currents, 
the  resistance  to  direct  currents  would  be  low,  while  the  same 
circuit  would  greatly  impede  the  flow  of  an  alternating  or 
varying  current,  the  extent  of  the  impedance  depending  upon 
the  inductance  of  the  coil,  the  limits  between  which  the 
amplitude  of  the  current  varies,  and  the  frequency  of  the 
alternations  or  variations. 

In  radio  signaling  systems  of  today  two  principal  kinds  of 
electric  wave  producers  are  in  general  use.  The  older  of 
these  is  the  spark  system,  with  which  electromagnetic  waves 
are  generated  by  the  spark  discharge  of  a  condenser.  The 
waves  are  sent  out  in  groups,  the  group  frequency  being  de- 

159 


160  RADIODYNAMICS 

pendent  upon  the  frequency  of  the  alternating  current  charg- 
ing the  condenser,  and  the  spark-gap  setting,  and  the  length 
of  the  waves  upon  the  electrical  sizes  of  the  condenser,  and 
the  inductance  through  which  it  discharges. 

The  number  of  waves  in  a  train  is  governed  by  the  damping 
of  the  circuit,  which,  in  turn,  depends  on  the  various  sources 
of  energy  loss,  such  as  heating,  and  radiation  of  electro- 
magnetic waves. 

For  example,  take  a  5oo-cycle  transmitter  emitting  a  1000- 
meter  wave.  The  5oo-cycle  alternator  is  connected  to  the 
condenser  circuit  through  a  step-up  transformer.  The  con- 
denser is  charged  during  the  first  half  of  each  alternation  of 
the  primary  current  and  discharges  across  the  spark  gap 
when  its  potential  reaches  the  necessary  value.  This  dis- 
charge occurs  at  the  peak  of  the  alternating-current  wave  in 
the  primary  circuit,  is  oscillatory  in  nature,  and  the  number 
of  oscillations  in  the  train  is  dependent  upon  the  damping. 
If  the  damping  is  small  15  oscillations  may  occur  in  the  de- 
cadent train  before  the  potential  drops  too  low  to  overcome 
the  resistance  of  the  spark  gap. 

The  time  during  which  the  discharge  takes  place,  therefore, 
with  a  looo-meter  wave  (300,000  frequency),  and  15  com- 
plete cycles  to  the  train,  would  be  -  —? —  of  a  second,  or  one 

150,000 

ten-thousandth  of  a  second.  Thus  with  the  5oo-cycle,  1000- 
meter  wave  transmitter,  once  in  each  one- thousandth  of  a 
second  the  condenser  discharges  for  one  ten-thousandth  of  a 
second,  producing  a  decadent  train  of,  say,  15  oscillations. 

The  other  type  of  transmitter  is  the  continuous  wave 
generator,  which  either  by  the  high-frequency  alternator  or 
the  Duddell-Thompson  arc,  produces  continuous  undamped 
waves.  The  waves,  instead  of  being  produced  in  decadent 
trains  during  only  one-tenth  of  the  time,  as  with  the  spark 
sets,  are  generated  continuously  and  with  constant  amplitude. 


THE  IN  TERFERENCE  PRE VEN  TER  1 6 1 

At  the  receiving  station  the  effects  produced  by  the  two 
types  of  wave  generators  is  somewhat  different. 

With  the  spark  set  the  oscillatory  currents  developed  in 
the  receiving  antennae  by  the  transmitter,  and  built  up  by 
resonance  are  rectified,  and  flow  through  the  indicating  in- 
strument. The  telephone,  which  is  used  as  the  indicating 
instrument,  therefore  receives  a  direct-current  impulse  for 
each  discharge  of  the  transmitting  condenser.  These  im- 
pulses, although  consisting  of  a  number  of  separate  impulses, 
act  as  one  pull  on  the  telephone  diaphragm,  which  vibrates 
at  a  rate  of  1000  times  per  second,  corresponding  to  the  trans- 
mitting group  frequency.  This  periodic  motion  produces  an 
acoustic  note  of  high  pitch.  Dots  and  dashes  are  distinguished 
by  the  length  of  time  during  which  the  note  is  produced, 
dots,  say,  one-tenth  second,  and  dashes  one-fifth  to  one-half 
second.  This  note  is  produced  in  the  receiving  telephone 
only  when  the  transmitting  key  is  closed. 

With  the  undamped  wave  transmitter  there  is  no  audible 
variation  in  the  received  rectified  current,  the  effect  of  which 
is  practically  the  same  as  that  of  a  continuous  direct  current 
in  the  receiving  telephone.  Therefore  a  continuous  pull  on 
the  diaphragm  results  so  long  as  the  sending  key  is  depressed. 

This,  then,  is  the  essential  difference,  from  a  low-frequency 
consideration,  between  the  effects  of  spark  transmitters  and 
undamped  wave  transmitters.  The  former  produces  a 
periodic  received  current,  while  the  latter  produces  a  constant 
received  current. 

At  present  radio  stations  using  these  different  systems  pro- 
duce considerable  mutual  interference.  By  the  use  of  suitable 
apparatus  we  may  differentiate  between  the  two  kinds  of 
effects  at  the  receiving  station,  and  thereby  secure  a  greater 
degree  of  selectivity.  « 

The  following  description  covers  methods  for  accomplishing 
the  desired  results,  with  particular  reference  to  the  circuit 


162 


RADIODYNAMICS 


arrangements  illustrated  by  the  drawings.  Figs.  91,  92  and 
93  show  graphically  three  common  types  of  radio  trans- 
mitters. 

Fig.  91  illustrates  a  spark  transmitting  set.  The  alter- 
nating-current generator  G  supplies  current  to  primary  P 
of  step-up  transformer  T,  through  the  controlling  key  K. 
Secondary  S  supplies  high  potential  current  for  charging 
condenser  C,  to  break  down  the  spark  gap  SG.  When  the 
potential  reaches  the  sparking  value,  C  discharges  across  SG, 
and  through  inductance  L,  and  by  electromagnetic  induction 
and  resonance,  an  oscillatory  current  is  set  up  in  the  radiating 
system  composed  of  antenna  A,  inductance  Li,  and  earth  E. 

$ 


JT 


FIG.  91. 


FIG.  92. 


In  Fig.  92  a  continuous  wave  transmitter  is  shown.  High- 
frequency  alternator,  H.F.A.,  sets  antenna  Ai  into  electrical 
vibration  by  means  of  coupling  coils  L2  and  L3,  as  is  common 
in  the  art.  The  antenna  is  earthed  at  E,  and  signals  are  sent 
by  making  a  condition  of  resonance  or  dissonance  between 
H.F.A.  and  the  tuned  radiating  system  Ai-I/j-Ei.  This  is 
accomplished  by  short-circuiting  or  otherwise  changing  the  in- 
ductance or  capacity  of  the  radiating  system  with  the  trans- 
mitter key  in  such  a  manner  as  to  produce  the  desired  signal. 
In  this  way  the  signals  may  consist  either  of  periods  of  work 
or  of  rest  of  the  radiator. 

Fig.  93  illustrates  an  undamped  wave  transmitter,  based 


THE  INTERFERENCE  PREVENTER 


on  the  principles  of  the  Duddell-Thompson  oscillatory  arc. 
The  direct-current  generator  Gi,  which  preferably  gives  a 
potential  of  about  500  volts,  supplies  direct  current  to  the 
electrodes  of  the  arc  AR,  through  the  choke  coils  L4  and  LS. 
When  properly  adjusted,  electric  oscillations  are  set  up  in  the 
closed  oscillatory  circuit,  comprising  arc  AR,  condenser  Ci, 
and  inductance  coil  L6,  the  frequency  of  which  is  determined 
principally  by  the  values  of  Ci  and  L6.  By  electromagnetic 
induction  and  resonance  oscillatory  currents  are  produced  in 
the  radiating  system  composed  of  antenna  A2,  inductance 
Ly,  and  earth  E2.  In  order  to  send  signals,  the  key  K2, 
which  establishes  resonance,  is  used. 


FIG.  93. 


FIG.  94. 


Figs.  94,  95  and  96  are  schematic  representations  of  re- 
ceivers based  on  the  idea  of  reducing  interference  between 
spark  and  undamped  wave  systems. 

Fig.  94  illustrates  the  circuit  arrangements  of  a  receiver 
for  use  with  an  undamped  wave  transmitter,  such  as  Fig.  92 
or  93. 

The  action  is  as  follows:  By  the  phenomenon  of  electric 
wave  propagation  and  reception,  when  the  transmitting  key 
is  closed,  alternating  currents  of  high  frequency  are  de- 
veloped in  the  resonant  receiving  antenna  system,  which  in- 
cludes antenna  A$,  inductance  L8,  condenser  C2,  and  earth 
£3.  Circuit  L9-C4-D  is  energized,  and  current  energy  is  sup- 


1 64  RA  DIOD  YNA  MICS 

plied  to  detector  D,  through  the  stopping  condenser  €4.  D 
is  a  detector  such  as  a  thermal  or  thermoelectric;  Lio  is  a 
choke  coil,  and  I  an  indicating  instrument  for  translating  the 
received  currents  into  effects  observable  with  one  or  more  of 
the  physical  senses.  D  produces  a  unidirectional  current  in 
the  circuit  D-Lio-I,  for  each  wave  train  impressed  upon  it. 
That  is,  for  signals  from  a  5oo-cycle  spark  transmitter,  D 
produces  a  pulsating,  unidirectional  current  in  the  indicating 
circuit,  the  frequency  of  which  is  1000  per  second,  equal  to 
the  transmitting  group  frequency,  and  for  signals  from  an 
undamped-wave  transmitter.  D  produces  a  unidirectional, 
unvarying  current  in  the  indicator  circuit.  Therefore  it  is 
obvious  that  the  distinguishing  difference  between  spark  and 
undamped-wave  signals  is  that  one  produces  a  periodic  re- 
ceived current,  while  the  other  produces  a  constant  received 
current.  The  detector  D,  it  must  be  understood,  has  too 
much  inertia  to  follow  the  high-frequency  impulses  of  the 
oscillatory  current,  which  are  of  the  order  of  500,000  per 
second,  but  it  can  and  does  follow  the  impulses  correspond- 
ing to  the  group  frequency,  which  need  not  be  greater  than 
1000  per  second.  This  inertia  or  lagging  action  is  due  to  the 
fact  that  detectors  of  this  class  which  are  operated  by  the 
heat  developed  by  the  incoming  oscillations,  cannot  heat  and 
cool  with  sufficient  rapidity  to  follow  the  enormously  high 
number  of  periodic  variations  in  the  heat-producing  current. 

Referring  now  to  Fig.  94,  choke  coil  Lio  is  of  such  value 
as  to  greatly  impede  the  flow  of  the  periodically  varying  cur- 
rents produced  by  spark  transmitters,  while  direct  currents 
set  up  by  continuous  wave  transmitters  flow  unimpeded. 
For  this  reason  the  interfering  effect  of  a  near-by  spark  station 
on  a  continuous  wave  receiving  station  is  greatly  reduced. 

Fig.  95  illustrates  another  method  of  securing  the  same 
freedom  from  disturbance.  The  receiving  antenna  system, 
composed  of  A4,  Ln,  C5,  and  £4  is  coupled  to  the  closed 


THE  INTERFERENCE  PREVENTER 


oscillatory  circuit,   comprising  Li2   and  C6,  with  which  it 

is  in  resonance.     Circuit  Li2-C6  supplies  oscillatory-current 

energy  to  detector  Di,  which  furnishes  unidirectional  current 

to  winding  W  of  indicating  the  instrument  and  to  primary 

Pi  of  transformer  Ti.      Secondary 

Si    is    connected    to    winding  Wi      A, 

through  stopping  condenser  C8,  and 

rectifier  T>2  rectifies  the  alternating    Ln 

current  supplied  by  Si  for  use  at 

Wi. 

The  indicating  instrument  is  here 
represented  as  a  relay  in  which  M 
is  the  moving  element,  but  any  other 


Cs 


FIG.  95. 


form  of  indicating  instrument  may  be  used,  or  W  and  Wi 
may  be  independent  primaries  of  an  induction  coil,  both  of 
which,  when  in  operation,  produce  equal  and  opposite  effects 
upon  a  secondary  coil,  connected  to  the  indicating  instru- 
ment, while  one,  operating  alone,  produces  the  signal  effect. 

The  operation  is  as  follows:  When  continuous  wave  signals 
are  received,  Di  supplies  unidirectional  currents  to  W  and 
Pi.  There  is  no  induction  of  current  into  Si,  because  the 
currents  in  Pi  do  not  vary,  and  therefore  only  W  of  Ii  is 
energized,  and  M  is  attracted,  i.e.,  the  relay  is  operated. 

If  periodic  currents  are  delivered  by  Di,  such  as  are  set 
up  by  spark  transmitters,  currents  are  induced  in  Si  and 
therefore  Wi  receives  direct-current  impulses  by  the  action 
of  D2  and  C8.  Now  Ti,  W,  and  Wi  are  so  proportioned  that 
with  spark  signals  of  the  common  frequencies,  the  magnetic 
effects  of  W  and  Wi  are  equal  and  opposite.  M  will,  there- 
fore, be  unaffected  when  group-frequency  signals  are  received, 
but  will  operate  without  difficulty  with  continuous  wave 
signals. 

Fig.  96  represents  the  circuit  arrangements  and  apparatus 
necessary  to  prevent  interference  from  continuous  wave 


i66 


RADIODYNAMICS 


transmitters  to  receivers  of  spark  signals,  such  as  are  pro- 
duced by  the  transmitters  of  Fig.  91.  Antenna  A6,  induc- 
tance Li6,  condenser  Ci2,  and  earth  E6,  form  the  receiving 
antenna  circuit.  Coupled  to  this  is  the  closed  circuit  com- 
posed of  inductance  Li7  and  ca- 
pacity Ci3.  The  two  circuits  are 
tuned  to  resonance  with  each  other 
and  with  the  transmitter.  When 
energized,  Li7~Ci3  supplies  energy 
to  detector  D4,  through  stopping 
condenser  Ci4.  D4  delivers  uni- 
directional currents  to  primary  P2 
of  transformer  T2.  Secondary  82 


Lie 


Ll7 


PQ* 


FIG.  96. 


is  connected  to  telephone  F2.  The  continuous  currents 
produced  in  the  circuit  D4-P2  by  continuous  wave  trans- 
mitters produce  no  induced  currents  in  82.  Therefore  F2 
does  not  operate  when  continuous  wave  signals  are  re- 
ceived. Spark  signals,  however,  produce  periodic  direct 
currents  in  P2,  which  by  induction  produce  alternating  cur- 
rents in  82  and  F2.  F2  therefore  receives  spark  signals  with- 
out difficulty,  but  remains  inoperative 
for  continuous  wave  signals. 

Fig.  97  is  a  schematic  representation 
of  a  thermal  detector  circuit.     D  is  the  IG<  97' 

fine  wire  of  the  thermal  detector,  which  is  connected  in  series 
with  choke  coil  Li8,  indicating  instrument  12,  and  a  source 
of  direct  current  Z,  which  is  a  battery  and  potentiometer. 

This  circuit  is  suitable  for  use  with  the  antenna  circuit 
shown  in  Fig,  94  for  the  continuous  wave  receiver. 


CHAPTER  XX 
DETECTORS 

According  to  the  definition  adopted  by  the  standardization 
committee  of  the  Institute  of  Radio  Engineers,  a  radio  de- 
tector is  "that  portion  of  the  receiving  apparatus  which,  con- 
nected to  a  circuit  carrying  currents  of  radio  frequency,  and 
in  conjunction  with  a  self-contained  or  separate  indicator, 
translates  the  radio-frequency  energy  into  a  form  suitable  for 
the  operation  of  the  indicator.  This  translation  may  be 
effected  either  by  the  conversion  of  the  radio-frequency 
energy,  or  by  means  of  the  control  of  local  energy  by  the 
energy  received." 

A  wrong  impression  relative  to  the  exact  function  of  a  de- 
tector in  a  wireless  receiver  has  been  prevalent  among  those 
engaged  in  radio  work.  This  misconception,  as  pointed  out 
by  Professor  Pierce,  is  that  detectors  are  more  sensitive  to 
electrical  energy  than  the  telephone,  galvanometer,  or  relay  is. 

Detectors  are  necessary  only  because  the  energy  of  the 
high-frequency  received  current  is  in  an  unsuitable  form  for 
use  with  the  indicating  instruments  employed.  This  is 
obvious  when  we  consider  such  instruments  as  the  Hetrodyne 
receiver  of  Fessenden's,  which  is  an  indicator  so  arranged 
that  the  high-frequency  currents  themselves  operate  it  —  no 
detector  or  translating  device  of  any  kind  being  required. 

Because  the  frequency  of  the  oscillations  is  so  high  (of  the 
order  of  a  million  per  second),  the  moving  coils  of  galva- 
nometers, the  diaphragms  of  telephones,  or  even  the  light 
fiber  of  the  Einthoven  string  galvanometer  cannot  follow  them. 
No  motion,  and  consequently  no  indication  therefore  results. 

167 


l68  RADIODYNAMICS 

The  energy  must  be  applied  either  in  such  a  form  that  it 
acts  in  one  direction  on  the  indicator,  as  required  in  the  tele- 
phone and  galvanometer,  or,  if  alternately  in  opposite  direc- 
tions, the  frequency  of  the  alternations  must  be  so  low  that 
the  inertia  of  the  moving  parts  of  the  indicator  does  not  come 
greatly  into  play.  In  the  case  of  the  telephone  this  frequency 
should  not  exceed  2000  per  second,  about  1000  per  second 
being  the  best  value;  with  the  Einthoven  string  galvanometer 
the  best  frequency  is  still  lower,  in  the  neighborhood  of  100 
per  second;  coil  galvanometers  have  such  a  slow  period,  about 
i  to  10  seconds,  that  they,  for  all  practical  purposes,  are  be- 
yond consideration  in  this  respect. 

True,  alternating-current  instruments  depending  on  the 
Thompson  effect  have  been  constructed,  which  give  uni- 
directional deflections  for  alternating  currents  of  radio  fre- 
quency, and,  like  the  Hetrodyne  receiver,  do  not  require  a 
detector,  but  they  are  so  insensitive  that  they  can  be  used 
only  where  comparatively  large  energies  are  received,  such 
as  in  the  wave-meter  application  by  Dr.  Seibt.* 

For  the  operation,  then,  of  our  common  and  most  sensitive 
indicators,  we  require  some  form  of  translating  device;  this  is 
not,  as  has  been  supposed,  for  the  reason  that  the  detector  is 
a  wonderfully  sensitive  instrument,  but  because  it  furnishes 
a  means  of  utilizing  the  marvelous  sensitiveness  of  these 
indicators. 

Taken  singly  the  detector  is  perhaps  the  most  important 
part  of  a  radiodynamic  system.  It  is  to  the  torpedo  what 
the  ear  is  to  a  telephone  operator;  all  orders  are  received 
through  it;  without  it  wirelessly  directed  torpedoes  would  be 
impossible,  just  as  the  telephone  would  be  impossible  with- 
out human  ears.  It  is  delicate,  necessarily,  because  of  the 
slight  effects  it  must  respond  to;  like  the  human  ear  it  must  be 

*  Elihu  Thompson,  Eke.  World,  May  28,  1887;  see  also  Proceedings  Inst. 
Radio  Engineers,  Vol.  i,  Part  3,  1913;  and  Phys.  Review,  Vol.  20,  p.  226,  1905. 


DETECTORS  169 

able  to  stand  up  under  heavy  cannonading  as  well  as  to  hear 
weak  signals  from  a  distance;  it  must  be  rugged  to  withstand 
the  severe  conditions  imposed;  rugged,  because  subject  to 
strong  effects,  both  mechanical  and  electrical,  which  tend  to 
break  down  its  original  sensitive  adjustment;  rugged  for  the 
reason  that  the  possibility  of  readjustment  in  a  dirigible 
torpedo  is  excluded. 

An  ideal  detector  is  one  that  is  extremely  sensitive,  and  at 
the  same  time  immune  to  disturbances  which  make  readjust- 
ment a  necessity;  one  that  will  operate  with  the  faintest 
signals,  as  well  as  stand  up  under  the  strongest  electrical  and 
mechanical  shocks. 

Although  close  approaches  have  been  made  to  this  ideal, 
the  perfect  detector  has  not  yet  been  produced.  Those  in 
use  purely  for  signaling,  i.e.,  radiotelegraphy  and  telephony, 
where  an  operator  is  constantly  in  attendance,  are  near 
enough  for  all  practical  purposes,  but  for  such  work  as  torpedo 
control,  they  are  not  yet  what  they  should  be.  Even  though 
the  best,  namely,  those  designed  or  modified  especially  for. 
this  purpose,  do  operate  perfectly  for  hours  at  a  time' under 
the  conditions  of  torpedo  control,  yet  they  cannot  be  de- 
pended upon  absolutely,  and  absolute  dependence,  absolute 
reliability  in  the  detector  are  pre-requisites  for  a  really  suc- 
cessful dirigible  torpedo. 

Since  the  first  electric  oscillator  of  Hertz,  which  consisted 
of  a  bent  wire  with  the  ends  very  near  together,  a  number  of 
different  types  of  detector  have  been  brought  out.  These 
new  types  and  modifications  have  been  steadily  improved  in 
sensitiveness  and  reliability. 

Detectors  may  be  classified  under  the  following  titles: 
Coherers.  Crystal  rectifiers. 

Magnetic  detectors.  Electrolytic  detectors. 

Thermal  detectors.  Electrometer  detectors. 

Thermoelectric  detectors.  Vacuum  detectors. 


1 70  RADIODYNAMICS 

A  further  classification  may  also  be  made  which  places 
detectors  under  one  of  two  general  heads,  namely,  potential 
operated  detectors  and  current  operated  detectors. 

The  following  table  gives  this  classification  according  to  the 
present  theories  of  operation  for  these  detectors: 

Potential  Operated  Current  Operated 

1.  Loose  contact  coherers.          Magnetic. 
(Filings,  Lodge-Muirhead,  mi-     Thermal. 

crophonic  contacts,  etc.)          Thermoelectric. 

2.  Capillary  electrometer.  Crystal  rectifiers. 

3.  Potentio  vacuum  detector.      Electrolytic  detectors. 

Vacuum  detectors. 

The  potential  group  operate  like  a  trigger  in  that  they 
control  local  sources  of  energy  which  effect  indicator  oper- 
ation, and  depend  on  the  potential  of  the  received  currents. 

The  current  operated  group  depend  upon  the  current 
effects  of  the  received  energy.  In  some  there  is  a  local  source 
of  energy  which  is  called  somewhat  into  play  by  the  action  of 
the  received  current.  The  bolometer,  which  comes  under  the 
thermal  class,  is  one  of  these.  In  others  the  oscillatory  energy 
alone  affects  the  indicator  operation.  Among  these  is  the 
crystal  rectifier,  which,  chopping  off  the  even  or  odd  alter- 
nations in  a  received  wave  train,  leaves  only  impulses  of  one 
sign,  positive  or  negative.  In  others  still,  both  the  incoming 
energy  and  local  energy  called  into  play  by  it  act  upon  the 
indicator.  The  crystal  rectifiers  with  a  local  battery  are 
•examples  of  these. 

For  torpedo  control  a  detector  must  be  able  to  withstand 
the  heavy  electrical  shocks  at  the  shortest  ranges,  and  at  the 
same  time  be  sufficiently  sensitive  to  operate  the  relay  at 
distances  up  to  eight  or  ten  miles.  In  addition  to  this  it 
must  not  be  affected  by  the  mechanical  vibration  and  shocks 
met  with  aboard  a  small  self-propelled  craft  in  a  rough  sea, 


DETECTORS  171 

and  remain  in  operative  adjustment  for  at  least  one  hour 
under  such  conditions. 

Coherers,  as  before  stated,  are  sufficiently  sensitive,  but 
their  action  is  erratic;  heavy  received  currents  cause  detri- 
mental effects;  as  a  whole,  they  are  far  from  the  solution  of 
the  detector  problem. 

Magnetic  detectors  are  very  stable,  both  electrically  and 
mechanically;  they  will  not  burn  out  with  the  strongest 
signals,  nor  lose  their  adjustment  when  subject  to  severe 
mechanical  shocks,  such  for  instance  as  those  arising  from 
heavy  gun  fire.  Their  failing,  however,  is  insensitiveness,  in 
which  they  are  below  most  detectors  in  use. 

Thermal  detectors,  such  as  Fessenden's  barreter  and  the 
bolometer,  are  mechanically  stable,  but  they  are  subject  to 
burnouts  from  strong  signals,  and  are  insensitive.  The  fine 
platinum  wire,  the  resistance  changes  in  which  arise  from  tem- 
perature variations  produced  by  the  oscillatory  currents  flow- 
ing through  it,  can  be  fused  by  received  currents  of  excessive 
intensity.  Immunity  from  these  burnouts  can  only  be  secured 
by  increasing  the  thickness  of  the  fine  wire,  but  this  again 
reduces  the  sensitiveness,  which  at  the  best  is  not  even  equal 
to  that  of  the  magnetic  detector. 

Thermoelectric  detectors  employing  a  junction  of  two  dis- 
similar metals,  such  as  bismuth  and  antimony,  which,  when 
heated  by  the  passage  through  it  of  oscillatory  currents, 
produce  direct  thermoelectromotive  forces,  have,  like  the 
magnetic  detector,  the  necessary  stability,  but  they,,  too,  are 
insensitive.  They  are  also  somewhat  handicapped  in  having 
a  comparatively  large  heat  capacity,  so  that  a  signal  several 
seconds  long  must  be  sent  before  the  temperature  of  the 
junction  rises  to  the  maximum  value  for  a  given  signal  in- 
tensity; likewise  it  requires  a  similar  length  of  time  for  cool- 
ing. DuddelPs  thermogalvanometer,  which  is  probably  the 
most  sensitive  of  the  combined  thermoelectric  detector  and 


172  RADIODYNAMICS 

galvanometer,  and  of  thermoelectric  detectors  in  general, 
though  valuable  for  the  purposes  of  measurements,  is  not 
sufficiently  rapid  or  sensitive  for  use  in  a  radiodynamic  system. 
Crystal  rectifiers,  sometime  called  also  solid  rectifiers, 
though  used  in  about  90  per  cent  of  radio  stations,  and  though 
more  sensitive  than  any  of  those  hitherto  described,  are  still 
too  low  in  sensitiveness  for  use  in  torpedo  control  work. 
This  has  been  previously  pointed  out  in  connection  with  the 
received  current  curve.  These  also  can  be  burned  out  by 
excessively  strong  signals,  so  that  readjustment  is  necessary, 
and  they  can  be  thrown  out  of  adjustment  by  vibration  or 
gun  fire. 

Electrolytic  detectors  are  about  equal  in  sensitiveness  to 
the  crystal  rectifiers,  but  are  not  so  much  used  as  they  were 
before  the  advent  of  the  crystal  rectifiers.  They,  too,  are 
subject  to  burnouts,  and  the  most  sensitive  types,  the  free 
point  electrolytics,  are  not  mechanically  stable.  The  glass 
point  electrolytic,  in  which  the  fine  wire  anode  is  sealed  in 
glass  and  immersed  in  the  acid  electrolyte,  though  not  possess- 
ing this  latter  defect  to  so  great  a  degree  is  less  sensitive  and 
is  also  subject  to  burnouts. 

The  capillary  electrometer  detector  (see  Fig.  98),  as  in- 
vented by  Armstrong  and  Orling  of  England,  consists  of  a 
minute  capillary  glass  tube  filled  with  mercury. 
The  small  end  of  this  tube  is  immersed  in  an 
acid  solution.     Under  the  action  of  a  current  the 
electrolytic  polarization  of  the  contact  causes  a 
change  of  the  surface  tension  of  the  mercury. 
Under  this  influence  the  mercury  rises  or  falls  in 
the  capillary  tube.    A  low-power  microscope  is 
used  to  observe  the  minute  motion  of  the  mer- 
cury column.     It  is  said  a  delicate  capillary  elec- 
trometer will  give  a  readable  deflection  with  an  applied  e.m.f. 
of  one  ten-thousandth  of  a  volt.     In  order,  however,  to  pro- 


DETECTORS  1 73 

duce  a  motion  sufficiently  to  act  as  a  relay  (one-sixteenth  inch), 
the  e.m.f.  must  be  increased  to  such  an  extent  that  the  sensi- 
tiveness is  too  much  reduced  to  make  the  instrument  of  value 
for  mechanism  control. 

Vacuum  detectors  *  have  previously  been  discussed  in  detail. 
Some  are  potential  operated,  others  are  current  operated, 
according  to  the  circuit  arrangements  employed.  It  has  been 
shown  that  with  a  suitable  form  of  circuit,  the  vacuum  de- 
tector approaches  nearer  the  ideal  by  far  than  any  other 


FIG.  99. 

detector.  Its  sensitiveness  is  as  much-  as  20  times  as  great 
as  the  best  of  other  detectors,  and  it  is  not  subject  to  burn- 
outs or  severe  mechanical  shocks.  It  is  this  detector  and 
the  circuit  which  makes  it  potential  operated  that  has  made 
possible  the  extraordinary  success  attained  by  Mr.  Hammond 
in  the  Gloucester  torpedo  control  experiments.  It  is  pictured 
in  Fig.  99  as  used  in  the  DeForest  System. 

The  hetrodyne  receiver  of  Fessenden,  depending  on  the 
principle  of  beats  for  its  operation,  cannot  be  used  for  relay 
operation,  but  the  beats  principle  can  be  applied  for  ampli- 
fication purposes.  This  will  be  described  in  another  chapter. 

*  For  detailed  accounts  of  the  very  important  work  recently  carried  out  by 
Dr.  Irving  Langmuir,  Dr.  Lee  DeForest,  and  others,  see  General  Electric  Review, 
March  1915,  May  1915,  and  Proceedings  Inst.  Radio  Engrs.,  Sept.  1915. 


174  RADIODYNAMICS 

The  frequency  transformer,  or  tone  wheel,  of  Dr.  Gold- 
schmidt  is  another  application  of  the  beats  principle.  Al- 
though a  very  efficient  form  of  detector  and  very  satisfactory 
for  telephones,  it  is  unsuitable  for  the  operation  of  our  most 
sensitive  relays,  which  require  direct  current,  because  it,  like 
the  hetrodyne,  produces  an  alternating  current  for  indicator 
operation.* 

*  For  complete  description  of  the  hetrodyne  receiver  and  U.  S.  Navy  test 
data,  see  Proc.  Institute  Radio  Engineers,  Vol.  i,  part  3,  1913;  a  complete 
description  of  the  Goldschmidt  frequency  transformer  is  contained  in  Proc. 
Inst.  Radio  Engrs.,  Vol.  2,  No.  i,  1914. 


CHAPTER   XXI 
METHODS   OF  INCREASING  RECEIVED   EFFECTS 

Various  means  for  increasing  the  intensity  of  received 
signals  have  been  proposed  and  utilized  within  the  past  ten 
years.  These  are  called  amplifiers,  amplifones,  variable  re- 
lays, intensifiers,  etc.,  but  the  generally  accepted  term  is 
amplifier.  It  may  be  defined  as  a  relay  which  modifies  the 
effect  of  a  local  source  of  energy  in  accordance  with  variations 
in  received  signals  and,  in  general,  produces  a  larger  indica- 
tion than  could  be  had  from  the  incoming  energy  alone. 

If  a  really  satisfactory  amplifier  were  available  the  serious- 
ness of  the  detector  problem  in  radiodynamics  would  be 
greatly  reduced,  for  then  a  receiving  detector  possessing  the 
necessary  stability,  though  lacking  in  sensitiveness,  could  be 
employed. 

To  fulfill  this  requirement,  an  amplifier  must,  first  of  all, 
be  capable  of  amplifying  with  a  high  ratio;  and,  next  in  im- 
portance to  this,  it  must  neither  be  subject  to  burnouts  nor 
mechanical  disturbances;  this  presupposes  no  necessity  for 
readjustment  for  at  least  several  hours;  simplicity  is  also  a 
very  desirable  element. 

Amplifiers  may  arbitrarily  be  classified  as  follows: 

1.  Microphonic  contact  amplifiers. 

2.  Generator  amplifiers. 

3.  Vacuum  tube  amplifiers. 

4.  Hetrodyne  amplifiers. 

Of  these  the  microphonic  contact  amplifiers  were  the  first 
to  be  developed,  and  they  are  most  used.  They  consist 

175 


176  RADIODYNAMICS 

essentially  of  a  combined  telephone  receiver  and  transmitter, 
the  same  diaphragm  serving  both.  The  rectified  received 
currents  flow  through  the  telephone  electromagnet  on  one 
side  of  the  diaphragm  the  consequent  vibratory  motion  of 
which  alters  the  resistance  of  the  adjustable  microphonic  con- 
tact on  the  opposite  side.  Those  in  use  for  radiotelegraphy 
usually  are  so  made  that  they  will  give  a  maximum  response 


FIG.  ioo. 

only  for  impulses  of  the  correct  group  frequency.  These  are 
called  spark-tuned  or  monotelephone  relays.  The  common 
types  employ  a  diaphragm  as  the  mechanically  tuned  element. 
The  Pickard,  Ruhmer,  Brown,  and  Telefunken  amplifiers  are 
examples  of  this  type.  Others  have  a  steel  reed  with  a  very 
pronounced  period  of  vibration,  to  increase  the  selectivity. 
Lowenstein  has  constructed  a  very  sensitive  instrument  of 
this  type.  The  instrument  devised  by  F.  C.  Brown  is  shown 
in  Figs,  ioo  and  101. 

This  type  of  amplifier  has  the  disadvantage  of  being  subject 
to  vibration,  jars,  and  sounds;   it  also  requires  frequent  ad- 


METHODS  OF  INCREASING  RECEIVED  EFFECTS        177 

justment.  Although  exploited  commercially  by  several  lead- 
ing radio  companies  it  has  never  been  extensively  adopted  for 
commercial  use,  even  for  radiotelegraphy. 

The  generator  amplifier  consists  of  a  small  generator  through 
the  field  coils  of  which  the  rectified  received  currents  are 
made  to  flow.  The  armature  currents,  with  all  the  charac- 
teristics of  the  field  currents,  but  much  amplified,  are  used 
for  indicator  operation.  Alexanderson  has  built  such  an 


FIG.  101. 
Connection  diagram  of  Brown  relay. 

amplifier,  which  he  designed  especially  for  telephony,  and 
succeeded  in  securing  amplification  ratios  as  high  as  20  to  i. 

It  is  believed  that  amplifiers  based  on  this  generator  prin- 
ciple present  the  most  satisfactory  solution  of  amplification 
problems.  They  are  not  subject  to  mechanical  disturbances; 
they  cannot  be  burned  out,  and  they  can  be  constructed  for 
high  amplification  ratios.  Driven  continuously  by  a  small 
electric  motor,  a  generator  amplifier  would  require  no  atten- 
tion or  adjustment.  They  also  lend  themselves  easily  to  spark 
tuning  when  a  variable  condenser  is  connected  across  the 
field  coils. 

Vacuum  tube  amplifiers  have  been  brought  out  independ- 
ently by  Lowenstein  and  DeForest.  With  three  vacuum  tube 


178  RADIODYNAMICS 

detectors  arranged  in  cascade  it  is  claimed  amplification  ratios 
as  high  as  120  to  i  have  been  obtained.  Such  an  arrange- 
ment is  shown  in  Fig.  102. 

These  instruments  though  possessing  a  high  amplification 
ratio,  and  not  greatly  affected  by  jars  or  vibration,  have  a 
multiplicity  of  adjustments  and  sometimes  are  thrown  out 
of  operation  by  very  strong  signals,  which  produce  the  familiar 
"blue  arc."  Although  not  so  desirable 
as  the  generator  amplifier,  they  are 
much  more  satisfactory  than  the  micro- 
phone amplifiers,  and  may  yet  be 
brought  to  the  desired  state  of  perfec- 
tion.* 

The  beats  principle  has  been  applied 
by  Fessenden  for  amplification  purposes 
in  radiotelegraphy. 

In  the  latest  form  of  this  receiver, 
which,  as  before  stated  in  the  chapter  on 
detectors,  is  called  the  Hetrodyne  re- 
ceiver, a  local  source  of  undamped  and 
variable  high-frequency  oscillations  is  arranged  so  as  to  act 
on  the  receiving  antenna  circuit,  and  so  adjusted  that  the  fre- 
quency of  its  alternations  is  very  nearly  equal  to  the  frequency 
of  the  incoming  waves .  The  effect  of  these  two  very  nearly 
equal  frequencies,  as  in  acoustics,  is  to  form  electrical  beats, 
or  alternate  additions  and  subtractions  of  the  two  independent 
forces,  of  a  periodicity  equal  to  the  difference  between  the  two 
original  frequencies. 

The  incoming  frequency  is  fixed,  but  the  local  frequency 
can  be  altered  at  will,  and  any  beat  frequency  desired  can  be 
produced  to  suit  the  acoustic  conditions. 

When  no  beats  are  produced  the  two  frequencies  are  equal; 

*  For  complete  description  of  the  DeForest  Audion  Amplifier,  see  Proc, 
Inst.  Radio  Engrs.,  Vol.  2,  No.  i,  1914,  page  24. 


METHODS  OF  INCREASING  RECEIVED  EFFECTS         179 

obviously  by  calibrating  the  local  source  of  oscillations,  a 
very  useful  means  of  measuring  the  exact  wave  length  of  a 
distant  transmitter  is  furnished. 

It  is  said  amplification  ratios  as  high  as  20  to  i  have  been 
secured  with  such  an  arrangement.  The  principal  difficulty 
with  this  system,  however,  is  a  reliable  generator  for  the  local 
oscillatory  currents  at  the  receiver.  Arcs  are  troublesome 
and  require  constant  attention;  high-frequency  alternators 
are  very  cumbersome  (existing  types  weighing  at  least  1000 
pounds,  and  possessiig  a  rotor  which  makes  20,000  r.p.m.) 
and  at  the  same  time  expensive.  For  this  reason  it  would 
be  next  to  impossible  to  utilize  this  amplifying  principle  for 
torpedo  control,  unless  some  simple  and  reliable  wave  gen- 
erator be  developed.* 

*  See  Proc.  Inst.  Radio  Engrs.,  Vol.  i,  Part  3,  1913.  The  author  in  1911 
under  the  direction  of  Mr.  Fritz  Lowenstein  experimented  successfully  with 
vacuum  tube  rectifiers  as  a  means  of  producing  sustained  high-frequency  os- 
cillations for  use  in  beat  amplifying  and  selective  systems  and  also  as  a  wave- 
generator  for  radio  telephony.  (For  a  very  complete  consideration  of  micro- 
phonic  contact  amplifiers,  see  extracts  from  a  paper  presented  before  the  I.  of 
E.E.,  London,  which  appeared  in  the  Elec.  Rev.  and  Western  Elect.,  Vol.  56, 
Nos.  23  and  24,  "A  Telephone  Relay,"  I  and  II.) 


CHAPTER  XXII 
RELAYS 

The  importance  of  a  relay  in  a  radiodynamic  system  is 
second  only  to  that  of  the  detector,  and  its  requirements  are 
just  as  exact.  That  is,  it  must  have  great  sensitiveness, 
ruggedness,  stability,  and  small  inertia. 

The  sensitiveness  necessary  in  the  relay  to  bridge  a  given 
distance  depends  upon  a  number  of  factors,  namely,  the 
height  and  power  in  the  transmitting  antenna,  and  the 
efficiency  of  the  receiving  detector,  or  detector  and  amplifier. 
Obviously  these  factors  must  be  taken  into  consideration 
for  the  reason  that  they  are  interdependent.  For  torpedo 
control  it  is  of  little  consequence  what  the  sensitiveness  of  any 
single  one  of  the  receiving  instruments  is  so  long  as  the  final 
result,  namely,  the  opening  and  closing  of  the  relay  contact, 
can  be  reliably  effected  from  the  transmitter  at  the  required 
distance,  and  so  long  as  the  combination  is  immune  to  dis- 
turbances of  whatever  nature  which  must  be  encountered. 
The  sole  function  of  the  detector,  amplifier,  and  relay  in 
mechanism  control  is  to  open  and  close  an  electric  circuit 
at  the  will  of  the  control  operator.  Any  combination  of  the 
above-named  instruments  that  will  accomplish  this  result 
with  absolute  reliability  is  a  satisfactory  solution  of  the  prob- 
lems involving  each  of  the  three  elements  separately.  That 
combination,  however,  which  is  most  simple,  least  cumber- 
some, and  least  expensive  is  to  be  preferred. 

In  radiodynamic  work  where  the  distance  is  not  limited 
by  vision,  as  it  is  with  torpedoes,  each  of  the  elements  should 
have  the  maximum  sensitiveness  in  order  that  the  distance 

180 


RELAYS  181 

of  operation  may  be  as  great  as  possible.  The  desirability 
of  this  is  evident  for  such  use  as  call-bell  operation  in  radio 
signaling. 

Relays  are  commonly  classified  as  polarized  and  non- 
polarized. The  motion  of  the  movable  element  in  the  former 
reverses  with  a  reverse  in  the  direction  of  the  current  energiz- 
ing it,  while  in  the  latter  the  motion  is  always  unidirectional. 

In  the  polarized  relays  either  an  armature  consisting  of  a 
permanent  magnet,  or  a  coil  through  which  the  current  flows, 
is  the  movable  element. 


No.   554. 


FIG.  103. 
Polarized  relay  of  the  high-resistance  type.     (Courtesy  J.  H.  Brunnell  &•  Co.) 

The  non-polarized  types  usually  have  a  soft  iron  armature 
or  core  which  is  always  attracted  in  one  direction  regardless 
of  the  direction  of  the  current  in  the  electromagnet  or  solenoid 
influencing  it. 

The  most  sensitive  non-polarized  relays,  such  as  those  used 
in  telegraph  offices,  require  a  current  of  three  or  four  milli- 
amperes  to  trip  them.  The  most  sensitive  of  the  polarized 
type,  as  developed  for  use  with  coherer  receivers  by  the 
Marconi,  Slaby-Arco,  Ducretet,  Telefunken,  and  other  com- 
panies, require  about  400  microamperes  under  operating  con- 


182  RADIODYNAMICS 

ditions.  Such  a  relay  is  shown  in  Fig.  103.  Movable  coil 
relays,  with  permanent  magnet  fields  and  solid  local  circuit 
contacts  as  previously  described  are  more  sensitive  than 
the  above  ferric  armature  types,  requiring  in  the  neighbor- 
hood of  200  microamperes  for  operation.  When  fitted  with 
strong  electromagnetic  fields  and  a  mercury-platinum  contact 
arrangement,  the  movable  coil  relays  can  be  made  to  operate 
reliably  on  from  about  30  to  5  microamperes,  depending  on 
the  mechanical  disturbances  encountered. 

A  very  sensitive  galvanometer  of  ordinary  construction 
and  about  1000  ohms  resistance  will  give  a  visible  deflection 
with  less  than  one  ten-millionth  of  a  volt,  but  such  an  instru- 
ment requires  a  very  solid  support,  such  as  a  heavy  masonry 
pillar,  and  the  slightest  vibration  or  current  of  air  will  cause 
the  delicately  suspended  coil  to  move.  Suspension  coil  gal- 
vanometers, though  possessing  very  high  sensitiveness,  can- 
not be  used  for  relays  because  of  their  extreme  delicacy. 
Even  uni-pivot  galvanometers,  such  as  the  portable  Paul 
instruments,  which  will  give  a  go-degree  deflection  for  10 
microamperes,  though  at  least  ten  times  as  sensitive  as  the 
author's  modification  of  the  Weston  dual-pivot  relay,  cannot 
be  used  for  relay  purposes  except  under  ideal  conditions  in 
the  laboratory.  They  require  leveling  screws,  and  though 
not  to  quite  so  great  a  degree  as  the  suspension  coil  galvanom- 
eter, are  still  much  too  delicate  for  use  aboard  a  torpedo. 

Likewise  galvanometers  of  the  vibration  type  like  Eintho- 
ven's,  which  are  capable  of  use  in  radio  receiving  stations  for 
recording  messages  photographically  over  great  distances,  are 
not  rugged  enough  for  torpedo  control  work. 

The  capillary  electrometer  can  be  used  as  a  relay,  but,  as 
before  stated,  its  sensitiveness  is  not  sufficiently  high. 

It  is  believed  that  the  remodeled  Weston  relay,  as  used  by 
Hammond,  is  the  most  satisfactory  instrument  for  this  kind 
of  work. 


CHAPTER  XXIII 
TORPEDO   ANTENNA 

It  is  not  the  purpose  here  to  discuss  the  many  details  in 
connection  with  the  ordinary  types  of  antenna  used  for  radio 
work  and  means  for  supporting  them.  I  wish  merely  to 
make  a  few  remarks  on  antennae  for  special  use  in  torpedo 
control  work,  and  briefly  to  describe  the  most  recent  pro- 
posals for  improvement  of  this  essential  part  of  the  receiving 
apparatus. 

Obviously,  as  shown  long  ago  by  Marconi,  the  receiving 
antenna  should  be  as  high  as  possible,  since  the  received  cur- 
rent increases  with  the  height.  Marconi  enunciated  at  one 
time  an  empirical  law  that,  for  simple  vertical  sending  and 
receiving  antennas  of  equal  height,  the  maximum  working 
telegraphic  distance  varied  as  the  square  of  the  height  of  the 
antennae.  The  experiments  of  the  General  Electric  Co.,  of 
Berlin,  also  roughly  agree  with  Marconi's  law.  Dr.  L.  W. 
Austin  has  worked  out  a  formula,  which,  taking  into  account 
the  antenna  heights  as  well  as  the  transmitting  power  and 
atmospheric  absorption,  gives  the  approximate  signaling 
range  of  any  transmitter  and  receiver.* 

The  length  of  the  horizontal  portion  of  an  antenna  is  also 
of  some  importance. 

We  see  then  that  for  our  torpedo  we  require  an  antenna  of 
the  greatest  possible  height  and  length.  It  is  very  doubtful 
whether,  with  the  type  of  craft  used  for  torpedoes,  this  height 

*  For  a  discussion  of  this  equation,  see  Austin,  L.  W.,  Bulletin  Bureau 
Standards,  1911,  Vol.  VII,  No.  3,  pp.  315-363,  "Some  Quantitative  Experi- 
ments in  Long  Distance  Radio  Telegraphy." 

183 


184 


RADIODYNAMICS 


could  be  made  to  exceed  the  length  of  the  vessel.  The  best 
practice,  as  shown  in  the  antennae,  in  use  on  the  submarine 
boats  of  the  navies  of  the  world,  substantiate  this  statement. 

I ,        The  40-foot  Radio  in  the  Gloucester 

experiments  had  a  three-wire  inverted 
L-type  antenna,  with  6-foot  spreaders 
of  light  bamboo;  it  was  about  20  feet 
above  the  water  and  about  thirty  feet 
long,  supported  by  two  3 -section  masts 
made  of  the  lightest  steel  tubing  con- 
sistent with  strength.  These  weighed 
about  15  pounds  each.  The  antenna 
wire  was  of  the  usual  phosphor-bronze 
variety  having  7  strands  of  No.  22 
wire.  A  single  1,000,000- volt  strain 
insulator  between  each  spreader  and 
mast-head  blocks  furnished  the  neces- 
sary overhead  insulation.  For  the 
leading-in  insulation  a  5oo,ooo-volt  roof 
type  leading-in  insulator  was  used. 
This  was  protected  from  the  flying 
spray  by  an  improvised  hood.  These 
insulation  precautions  were  taken  as  a 
result  of  experiments  which  proved 
their  necessity  with  the  potential- 
operated  vacuum  detectors. 

Experiments   were   made   with   this 
antenna  in  the  effort  to  increase  its 
effective    length.      By    increasing    its 
length  it  would  be  possible  to  increase 
its  natural  wave  length  and  thus  di- 
minish the  value  of  the  energy  absorbing  loading  inductances 
necessary  for  tuning  to  the  transmitted  waves. 
In  this  connection  a  field  worthy  of  experimentation  is  one 


FIG.  104. 

Common  type  of  radio 
tower. 


TORPEDO  ANTENNAE  185 

which  covers  the  possibilities  relative  to  variation  of  trans- 
mitting wave  length  between  two  antennae  of  widely  different 
natural  periods. , 

It  is  well  known  that  a  transmitting  antenna  will  operate 
most  efficiently  only  at  that  wave  length  corresponding  to 
the  natural  period  of  the  antenna  with  just  sufficient  induc- 
tance in  series  for  coupling  to  the  closed  circuit.  If  the  wave 
length  be  increased  energy-absorbing  loading  inductances  are 
necessary;  if  decreased,  an  energy-absorbing  series  capacity 
must  be  used. 

The  receiving  oscillatory  system  likewise  has  a  definite 
wave  length  for  which  it  will  operate  most  efficiently,  and  for 
the  same  reasons.  It  is  known,  however,  that  the  current  in 
an  oscillatory  circuit  is  inversely  proportional  to  the  wave 
length,  so  that  although  the  receiving  antenna  is  operating 
inefficiently  at  a  wave  length  below  its  natural  wave  length, 
it  is  possible  that  the  receiver,  as  a  whole,  works  at  an  in- 
crease in  efficiency.  Again,  while  the  receiver  works  best 
with  short  wave  lengths,  the  power  that  can  be  handled  by  a 
transmitting  antenna  decreases  with  its  natural  wave  length, 
and  so  it  is  possible  that  the  large  transmitting  powers  made 
possible  by  high,  large  capacity,  long  wave  length  antennae 
will  entirely  overbalance  the  detrimental  effects  due  to  in- 
efficiency in  the  reception  of  the  waves.  This  presents  an 
interesting  field  for  experimentation.* 

At  the  suggestion  of  Dr.  Lee  DeForest,  the  "Radio's" 
antenna  was  fitted  with  an  extension  in  the  form  of  two  long 
wires  attached  to  the  after  spreader  and  reaching  down  to  a 
light  wooden  float  30  or  40  feet  astern;  the  swift  motion  of  the 
boat  kept  the  wires  taut.  Long  pennant-like  pieces  of  cloth 

*  See  "Optimum  Wave-length  in  Wireless  Telegraphy,"  by  A.  H.  Taylor, 
Physical  Review,  Vol.  i,  No.  4,  Apr.  1913,  pp.  321-325.  Also,  "Determination 
of  Wave-length  in  Radio  Telegraphy,"  A.  S.  Blatterman,  Electrical  World, 
Vol.  64,  No.  7,  Aug.  15,  1914,  pp.  326-329. 


l86  RADIODYNAMICS 

through  which  light  wires  connected  to  the  rear  end  of  the 
antenna  were  woven,  and  which  stood  out  almost  horizontally 
from  the  mast  head  when  the  boat  was  in  motion,  were  also 
tried.  Neither  method,  however,  was  found  of  any  material 
benefit. 

Water  Antenna.  A  very  novel  form  of  antenna  was  in- 
vented several  years  ago  by  Fessenden.  It  consists  of  a 
stream  of  water  thrown  vertically  upward  through  a  coil  of 
copper  tubing  by  a  centrifugal  force  pump.  Although  possi- 
bly inoperative  in  fresh  water  a  torpedo  so  equipped  might  be 
practicable  in  salt  water,  which  has  a  higher  conductivity. 
The  hollow  coil  serves  as  a  means  of  coupling  the  water 
antenna  to  the  receiving  apparatus. 

The  apparent  advantage  of  such  an  aerial  conductor  is  that 
it  cannot  be  shot  away  by  the  enemy.  No  data  relating  to 
actual  use,  either  experimental  or  practical,  of  an  antenna 
of  this  type  can  be  found. 

The  U.  S.  Navy  has  experimented  with  submerged  receiving 
antennas,  for  use  in  signaling  to  submarine  boats  equipped 
with  radio  apparatus.  The  antenna  consisted  of  a  type  of 
conductor,  very  heavily  insulated  with  rubber  and  other  in- 
sulating compounds,  known  as  "rat- tail."  The  antenna  wire 
was  thus  completely  insulated  from  the  water,  although  be- 
neath its  surface.  The  author  assisted  in  these  tests  which 
were  made  at  Washington,  in  1909.  Audible  signals  were 
received  with  such  an  antenna  in  the  Potomac  river  at  Alex- 
andria, Va.,  about  seven  miles  from  the  two-kilowatt  trans- 
mitter at  the  Washington  Navy  Yard. 

These  tests  after  considerable  experimenting  at  Charleston 
and  Boston  with  submarine  boats  were  finally  discontinued. 

Another  type  of  antenna,  which  has  a  marked  directive 
effect,  and  experimented  with  by  Dr.  Franz  Kiebitz,  of  the 
General  Telegraph  Department,  of  Berlin,  has  aroused  con- 
siderable interest  within  the  past  two  years.  A  straight  wire 


TORPEDO  ANTENNA  iSj 

is  stretched  horizontally  a  few  feet  above  the  earth,  and  the 
receiving  apparatus  connected  in  the  middle.  The  best 
directions  of  reception  are  those  to  which  the  free  ends  of  the 
wire  point.  In  other  forms  the  two  ends  are  grounded;  in 
still  others  only  one  end  is  grounded,  the  receiving  apparatus 
being  connected  near  that  end.* 

*  See  Proc.  Inst.  Radio  Engrs.,  Dec.  1915:  "  The  Effectiveness  of  the  Ground 
Antenna  in  Long  Distance  Reception." 


CHAPTER   XXIV 

RECENT  DEVELOPMENTS 

Pneumatic  Steering  Apparatus.  —  The  latest  development 
in  torpedo-control  apparatus  has  been  to  discard  electric 
steering  gear,  and  to  adopt  apparatus  designed  for  use  with 


FIG.  105. 

•The  head  telephones  enable  the  operator  to  listen  to  the  control  impulses;  the 
instrument  in  front  of  the  operator  is  a  searchlight  control  apparatus. 

compressed  air.  In  Figs.  105  and  106  may  be  seen  a  control 
operator  at  the  Hammond  Laboratory.  Fig.  107  is  a  view 
of  this  Laboratory,  and  Fig.  108  is  a  view  of  Hammond's 
latest  boat. 

188 


RECENT  DEVELOPMENTS 


189 


This  change  has  made  possible  a  great  simplification  of 
apparatus,  and  a  corresponding  increase  in  reliability;  inci- 
dentally it  has  also  increased  the  accuracy  of  control  because 
of  the  swiftness  with  which  the  operations  are  performed. 


FIG.  106. 

The  gratifying  results  now  being  secured  with  pneumatic 
apparatus  are  ample  evidence  of  the  truth  of  the  afore- 
mentioned statement  that  simplicity  is  a  highly  important 
factor  in  apparatus  where  adjustment  is  not  possible;  and 
that  even  very  simple  electric  devices  are  uncertain  in  their 
action. 
There  are  only  three  operations  necessary  for  the  control 


igo 


RADIODYNAMICS 


of  a  dirigible  torpedo,  namely:   (i)  rudder  to  port,  (2)  rudder 
to  starboard,  and  (3)  engine  control.     The  following  is  one 


FIG.  107. 

of  a  number  of  pneumatic  systems  devised  by  the  author 
with  this  " simplicity"  idea  in  mind.     In  addition   to  the 


FIG.  108. 


simple  and  rugged  nature  of  the  apparatus  it  also  possesses 
the  advantage  that,  unlike  other  systems,  it  does  not  require 


RECENT  DEVELOPMENTS 


191 


an  especially  trained  operator;  even  with  the  simplest  of  the 
old  systems,  such  as  Gardner's  and  Hammond's,  a  very  con- 
siderable amount  of  practice  is  necessary  in  order  to  attain 
expertness  in  the  boat's  control. 

This  system  was  designed  in  1912  for  use  with  selector 
systems  in  which  a  gradual  back  and  forth  rectilinear  motion 
of  the  movable  selector  element,  as  distinguished  from  the 


Wire/ess  Controlled 


Rudder 


FIG.  109. 

step  by  step  circular  motion  of  some,  can  be  secured.  Three 
of  the  author's  methods  as  well  as  that  of  Gardner's,  are 
adaptable  for  this  purpose. 

As  shown  in  Fig.  109  the  function  of  the  movable  selector 
element  is  to  control  air  valves,  which  in  turn  control  the 
energy  used  in  performing  the  desired  operations.  A  brief 
description  will  serve  to  explain  the  action  of  the  apparatus. 

Normally  the  transmitting  impulses  are  of  such  character 


IQ2  RADIODYNAMICS 

that  the  valve  V  is  partially  open,  thus  allowing  compressed 
air  to  escape  from  the  tank  to  the  cylinder.  At  this  normal 
position  the  pressure  inside  the  cylinder  reaches  a  certain 
value  and  then  remains  constant,  due  to  the  pull  of  the 
large  spring  S,  and  to  the  action  of  the  adjustable  escape 
valve  E.  If  the  valve  V  is  opened  wide  the  piston  moves 
quickly,  and  with  great  power  to  the  left,  due  to  the  fact 
that  the  escape  valve  cannot  take  care  of  this  increased 
inrush  of  air;  if  the  valve  is  closed  farther  than  the  normal 
position,  the  piston  will  be  moved  in  the  opposite  direction 
by  the  spring  S.  By  this  means,  the  rudder,  as  shown,  can 
be  made  to  move  to  either  side  as  swiftly  or  as  slowly  as  de- 
sired, and  maintained  in  any  position,  simply  by  altering  the 
position  of  the  steering  wheel  at  the  transmitting  station. 
This  alters  the  speed,  or  the  ratio  of  on  to  off  periods,  of  the 
impulses.  Thus  any  inexperienced  operator  can  steer  the 
boat. 

For  engine  control  a  rotary  valve  (not  shown)  operated  by 
the  solenoid,  is  used.  This  has  but  two  kinds  of  positions 
corresponding  to  start  and  stop.  When  it  is  desired  to  start 
the  engine,  one  turn  of  the  steering  wheel  to  the  extreme 
right  (farther  than  for  the  hard  over  position)  is  made;  the 
operation  for  stopping  is  exactly  the  same.  This  can  be 
done  quickly  so  that  no  interference  with  the  steering  evolu- 
tioned  need  be  experienced.  The  required  air  pressure  is 
maintained  in  the  tank  by  a  compressor  actuated  by  the 
propelling  motor. 

Another  system  of  the  writer's  depends  on  the  selecting 
action  of  a  dash-pot  retarded  solenoid  apparatus.  By  send- 
ing an  impulse  of  one  second,  then  allowing  a  short  break, 
and  then  holding  the  impulse  again,  number  one  circuit  can 
be  operated.  For  the  other  circuits  the  first  impulse  need 
only  be  changed  to  2,  3,  4,  etc.,  seconds,  according  to  the 
number  of  the  circuit  to  be  operated.  The  circuit  continues 


RECENT  DEVELOPMENTS  IQ3 

to  be  closed  as  long  as  the  last  impulse  is  held;  when  it  is 
stopped  the  selector  arm  returns  to  the  normal  position. 

Not  mentioning  the  work  now  being  carried  on  both  in  the 
United  States  and  in  Europe  on  the  control  of  trains  by 
control  systems  based  on  electromagnetic  induction  at  dis- 
tances of  a  few  feet,  the  latest  development  along  the  lines 
of  distant  control  has  been  reported  from  France  and  Italy 
in  connection  with  the  "F  ray"  naval  experiments  made  in 
the  Solent.  It  may  be  worth  recalling  that  Signor  Ulivi 
made  a  number  of  experiments  in  the  presence  of  the  French 
authorities  at  Villers-sur-Mer  in  August  of  1913. 

"The  'F  rays'  were  originally  discovered  by  a  professor  at 
the  University  of  Nancy,  and  there  has  been  considerable 
controversy  from  time  to  time  as  to  their  potency,  and  some 
have  even  doubted  their  existence.  On  the  other  hand,  ac- 
cording to  certain  reports,  the  effects  obtained  by  Signor 
Ulivi  were  wonderful,  and  amazed  the  French  authorities. 
No  less  a  personage  than  General  Joffre  is  said  to  have  been 
impressed  by  them,  and  to  such  an  extent  that  he  asked  the 
inventor  to  prepare  a  plan  by  means  of  which  an  enemy's 
magazines  and  powder  supplies  might  be  blown  up  from  a 
distance. 

"What  Signor  Ulivi  has  since  done  in  France  has  remained 
a  profound  secret;  in  fact  it  is  not  known  whether  he  has  done 
anything  at  all.  Immediately  after  the  first  articles  had 
appeared  in  the  papers,  in  August  of  1913,  it  is  understood 
he  was  asked  to  go  to  England  to  submit  some  tests  to  the 
British  Admiralty.  His  experiments  in  France  were  chiefly 
carried  out  at  Havre  and  Villers-sur-Mer.  They  were  wit- 
nessed by  General  Joffre,  General  Curieres,  de  Castelnau, 
Major  Ferrie,  and  a  delegate  of  the  Minister  of  War,  Captain 
Cloitre.  The  first  tests  consisted  of  a  series  of  submarine 
mines  of  which  there  were  ten,  placed  at  intervals  of  600 
meters.  Signor  Ulivi,  at  i  the  appointed  moment,  touched 


IQ4  RADIODYNAMICS 

a  lever,  and  one  by  one  the  mines  exploded  without  any 
visible  agent.  He  declared  that  he  had  done  it  by  a  con- 
centration of  the  power  of  F  rays.  He  was  next  asked  to 
blow  up  some  powder  magazines  in  an  old  hulk,  which  he 
also  did  successfully. 

"  The  technical  officers  who  had  witnessed  the  tests  next 
wanted  to  prepare  mines  in  their  own  way  and  defied  him  to 
explode  them.  This  he  is  alleged  to  have  refused  to  do  at 
one  moment,  and  a  discussion  arose.  Were  the  experiments 
sincere  or  not?  The  question  was  asked  and  sides  were  taken 
at  the  time;  but  the  dispute  was  suddenly  hushed  up  or 
dropped.  The  fact  is  that  every  subsequent  move  of  Signor 
Ulivi  has  been  shrouded  in  mystery."* 

Self-Directing  Torpedoes. 

The  latest  tendencies  along  torpedo-control  lines  have  been 
towards  the  development  of  apparatus  which  will  give  a  tor- 
pedo the  power  of  self -direction. 

In  1912  the  author,  in  collaboration  with  John  Hays  Ham- 
mond, Jr.,  developed  such  an  apparatus,  which  was  called 
an  " orientation  mechanism."  It  is  more  generally  known 
now  as  the  "electric  dog."  It  is  shown  in  Figs,  no,  in 
and  112. 

"This  orientation  mechanism  in  its  present  form,  consists 
of  a  rectangular  box  about  three  feet  long,  one  and  a  half 
feet  wide,  and  one  foot  high.  This  box  contains  all  the  in- 
struments and  mechanism,  and  is  mounted  on  three  wheels, 
two  of  which  are  geared  to  a  driving  motor,  and  the  third, 
on  the  rear  end,  is  so  mounted  that  its  bearings  can  be  turned 
by  electromagnets  in  a  horizontal  plane.  Two  five  inch 
condensing  lenses  on  the  forward  end  appear  very  much  like 
large  eyes. 

*  Extract  from  an  article  in  the  "London  Times." 


RECENT  DEVELOPMENTS 


195 


"If  a  portable  electric  light  be  turned  on  in  front  of  the 
machine  it  will  immediately  begin  to  move  toward  the  light, 
and,  moreover,  will  follow  that  light  all  around  the  room  in 
many  complex  manoeuvers  at  a  speed  of  about  three  feet  per 


Pony  Relay 


Wiring  Diagram-  Electric  Dog 
FlG.    I 10. 

second.  The  smallest  circle  in  which  it  will  turn  is  of  about 
ten  feet  diameter;  this  is  due  to  the  limiting  motion  of  the 
steering  wheel. 

Upon  shading  or  switching  off  the  light  the  dog  can  be 
stopped  immediately  but  it  will  resume  its  course  behind  the 


RADIODYNAMICS 


moving  light  so  long  as  the  light  reaches  the  condensing 
lenses  in  sufficient  intensity. 

"  The  explanation  is  very  similar  to  that  given  by  Jaques 
Loeb,  the  biologist,  of  reasons  responsible  for  the  flight  of 
moths  into  a  flame.  According  to  Mr.  Loeb's  conclusion, 
which  is  based  on  his  researches,  the  moth  possesses  two 
minute  cells,  one  on  each  side  of  the  body.  These  cells  are 
sensitive  to  light,  and  when  one  alone  is  illuminated  a  sensa- 


FlG.    III. 

Interior  of  Electric  Dog. 

tion  similar  to  our  sensation  of  pain  is  experienced  by  the 
moth;  when  both  are  equally  illuminated,  no  unpleasant 
sensation  is  felt.  The  insect  therefore  keeps  its  body  in 
such  a  position,  by  some  manner  of  reflex  action,  as  will  in- 
sure no  pains,  and  in  this  position  the  forward  flying  motion 
will  carry  it  directly  toward  the  source  of  light. 

"The  orientation  mechanism  possesses  two  selenium  cells, 
corresponding  to  the  two  light  sensitive  organs  of  the  moth, 
which,  when  influenced  by  light  effect  the  control  of  sensitive 
relays,  instead  of  controlling  nervous  apparatus  for  pain  pro- 


RECENT  DEVELOPMENTS  197 

duction,  as  is  done  in  the  moth.  The  two  relays  controlled 
by  the  selenium  cells  in  turn  control  electromagnetic  switches 
which  effect  the  following  operations;  when  one  cell  or  both 
are  illuminated  the  current  is  switched  onto  the  driving 
motor;  when  one  cell  alone  is  illuminated,  an  electromagnet 
is  energized  and  effects  the  turning  of  the  rear  steering  wheel. 
The  resultant  turning  of  the  machine  will  be  such  as  to  bring 
the  shaded  cell  into  the  light.  As  soon  and  as  long  as  both 


FIG.  112. 
Electric  Dog  in  Action. 

cells  are  equally  illuminated  in  sufficient  intensity,  the  ma- 
chine moves  in  a  straight  line  toward  the  light  source.  By 
throwing  a  switch,  which  reverses  the  driving  motors  con- 
nections, the  machine  can  be  made  to  back  away  from  the 
light  in  a  most  surprising  manner.  When  the  intensity  of 
the  illumination  is  so  decreased  by  the  increasing  distance 
from  the  light  source,  that  the  resistances  of  the  cells  approach 
their  dark  resistances,  the  sensitive  relays  break  their  respec- 
tive circuits,  and  the  machine  stops. 
"The  principle  of  this  orientation  mechanism  has  been 


198  RADIODYNAMICS 

applied  to  the  Hammond  dirigible  torpedo  for  demonstrat- 
ing what  is  known  as  attraction  by  interference.  That  is, 
if  the  enemy  tries  to  interfere  with  the  guiding  station's  con- 
trol, the  torpedo  will  be  attracted  to  it.  The  torpedo  is  fitted 
with,  apparatus  similar  to  that  of  the  electric  dog,  so  that  if  the 
enemy  turns  their  search  light  on  it,  it  will  immediately  be 
guided  toward  that  enemy  automatically. 

"In  order  that  the  search  light  used  by  the  control  opera- 
tor may  not  have  this  same  effect,  use  is  made  of  a  gyroscope 
to  keep  the  turn  table  upon  which  the  cells  are  mounted, 
in  a  fixed  position  relative  to  the  earth.  In  this  way  no  mat- 
ter how  much  the  torpedo  turns,  or  in  what  direction  it  is 
traveling  the  selenium  cells  will  always  face  from  the  shore 
and  toward  the  attacking  battleship  in  the  open  sea. 

"By  means  of  two  directive  antennae,  instead  of  two  sele- 
nium cells  the  same  principle  may  be  applied  for  attraction 
by  interference  when  Hertzian,  instead  of  light  waves  are 
used.  Sound  waves  might  also  be  utilized  in  a  similar  man- 
ner so  that  the  sound  reaching  the  torpedo  (which  would  be 
equipped  with  two  submerged  microphones  made  sensitive 
and  directive  by  megaphone  attachments)  from  the  pound- 
ing of  the  battleships  engines  and  other  machinery,  would 
effect  its  attraction  in  a  way  analogous  to  the  attraction  of  a 
source  of  light  for  the  orientation  mechanism.  It  is  just 
possible,  too,  that  similar  apparatus  could  be  used  for  the 
detection  of  submarines,  or  for  defense  against  them.'7 

The  electric  dog  operates  in  a  single  plane,  the  horizontal; 
the  author  has  developed  plans  for  extending  its  operations 
to  both  horizontal  and  vertical  planes,  by  using  two  sets  of 
the  orientation  apparatus  operating  at  right  angles  to  one 
another.  These  plans  include  the  use  of  all  forms  of  radiant 
energy. 

*  Extract  from  a  paper  on  Torpedo  Control  by  the  author  in  the  Purdue 
Engineering  Review,  1914. 


RECENT  DEVELOPMENTS  199 

With  such  a  double  orientator  a  new  defense  against  the 
submarine  becomes  possible.  Captain  K.  0.  Leon  of  the 
Swedish  navy  has  already  applied  the  electric  dog  principle 
to  the  automatic  direction  of  torpedoes,  the  soun4  waves 
sent  out  through  the  water  from  the  hull  of  a  ship  acting  as 
the  attracting  stimulus;  it, is  but  a  step  to  apply  a  double 
"orientator  of  this  type  to  torpedoes  that  will  seek  out  and 
destroy  any  submarines  within  its  range  of  hearing.  This 
same  type  of  automatic  director  is  suitable  for  use  with 
aerial  torpedoes,  explosive-laden  mechanical  moths,  which 
will  sweep  down  upon  the  ships  of  the  air  with  a  sting  that 
will  blow  them  into  a  thousand  pieces.  The  electric  dog 
which  now  is  but  an  uncanny  scientific  curiosity  may  within 
the  very  near  future  become  in  truth  a  real  "dog  of  war," 
without  fear,  without  h^art,  without  the  human  element  so 
often  susceptible  to  trickery,  with  but  one  purpose;  to  over- 
take and  slay  whatever  comes  within  range  of  its  senses  at 
the  will  of  its  master. 


INDEX 


Adams,  Prof.,  experiments  of,  in 
electromagnetic  induction  signal- 
ling, 15. 

Amplifiers,  classification  of,  175. 
De  Forest's,  50. 
Generator,  177. 
Hetrodyne,  178. 
Lowenstein's,  62. 
Microphonic,  175. 
Monotelephonic,  141. 
Vacuum  tube,  177. 
Antennae,  Austin's  law  for  height  of, 

183. 

Circuit  adjustment  of,  134. 
Marconi's  law  for  height  of,  183. 
Of  Kiebitz,  186. 
On  "Pioneer"  125. 
On  "Radio"  185. 
Submerged  receiving,  186. 
Torpedo,  183. 
Water  (Fessenden),  186. 
Armstrong  and  Orling,  capillary  elec- 
trometer, 172. 

Austin,  Dr.  L.  W.,  experiments  by, 

with  radiotelegraphic  sender,  72. 

Formula   of,   for    antennae   height, 

183. 
Automatic  recording  telegraph,  3. 

Balloon,  dirigible,  of  Roberts,  86. 
Battle-range  torpedo  control,  124. 
Bell,  Alexander  Graham,  experiments 
of,  in  electromagnetic  induction 
signalling,  15. 
Photophone  of,  9. 
Plan  of,  for  marine  signalling,  17. 
Beck,  experiments  of,  in  torpedo  con- 
trol, 100. 


Berger,   H.   Christian,   apparatus  of, 

in  earth  conduction,  71. 
Bolometer,  10,  41,  51. 
Boys,  radiomicrometer  of,  51. 
Branley,  codal  selector  of,  141. 

Control  system  of,  105. 

Protective  device  of,  106. 
Branly,    experiments    with    Hertzian 

waves,  27. 

"Branly  tube,"  or  coherer,  28. 
Bull,  Anders,  codal  selector  of,  141. 

Capillary  electrometer  (Armstrong  & 
Orling),  172. 

As  relay,  182. 
Cells,  silenium,  57. 

Selectivity  of,  63. 
Codal  selector,  of  Anders  Bull,  141. 

Branley,  141. 

Walter,  141. 

Wirth,  141. 
Coherers,  171. 

Branly's,  28. 

Control  energy,  choice  of,  34. 
Control  systems,  classification  of,  89. 

Beck's,  100. 

Branley's,  105. 

Deveaux's,  96. 

Hammond's,  of  torpedoes,  122. 

Knauss's,  TOO. 

Wirth's,  100. 

Cooke,  W.  F.,  needle  telegraph  of,  3. 
Crooke's  radiometer,  10,  51. 
Crystal  rectifiers,  172. 
Current,  density  of,  8,  9. 

d'Arsonval,  radiomicrometer  of,  51. 
Davy's  sound-relaying  system,  10,  n. 


201 


2O2 


INDEX 


De  Forest,  amplifier,  50. 

Vacuum-tube  rectifier,  129. 
Density   of    current   between    earth- 
plates,  8,  9. 
Detectors,  167. 

Capillary  electrometer,  172. 

Electrolytic,  172. 

Ion  controller  (Lowenstein),  24. 

Magnetic,  171. 

Potentio,  134. 

Radiant  heat,  46. 

Thermal,  171. 

Thermoelectric,  48,  171. 

Vacuum,  173. 

Deveaux's  dirigible  torpedo  boat,  96. 
Diathermanous  materials,  45. 
Dirigible    torpedo    boat    (Deveaux), 

96. 
Dolbear,    Prof.,    electrostatic   system 

of,  19. 

Double  orientation  mechanism,  194. 
Duddell's    thermogalvanometer,     10, 

171. 

Duddell-Thompson    arc,     142,     147, 
160,  163. 

Earth  conduction,  3,  67. 

Experiments    in    selective    control, 
offered  by,  67. 

Low  resistance  of,  8. 

Plan  of  Berger,  71. 

Plates  (Steinheil),  9. 
Edison,  dirigible  torpedo  c/,  86. 

"Tasimeter"  of,  10,  52. 
"Electric  Dog,"  194. 
Electric  wave  producers,  159. 
Electrolytic  detector,  172. 
Electromagnet,  invention  of,  3. 
Electromagnetic  induction,  76. 

Laws  of,  3. 

Telegraph,  3. 

First  overland  system  of,  3. 
Development  of,  4. 

Signalling,  15. 


Electromagnetic  sounder,  4. 
Wave  systems,  27. 

Later  improvements  in,  32. 
Marconi,    early   experiments   of, 

Tesla,  experiments  of,  28. 
Electrometer,  capillary,  172. 

As  relay,  182. 
Electrons,  effect  of  ultra-violet  rays 

on,  64. 

Electrostatic  telegraph  systems,  10. 
Of  Le  Sage,  4. 
Of  Lowenstein,  23. 

Electrostatic  and  electromagnetic  in- 
duction, 74. 

"F  Ray,"  discovery  of,  193. 

Experiments  of  Uiivi  in,  193. 
Faraday,   discovery  of  laws  of  elec- 
tromagnetic induction  by,  3. 
Fessenden,  Prof.,  hetrodyne  receiver 

of,  167,  173,  178. 
Interference  preventer  of,  142. 
Submarine  signalling  system  of,  36. 
Water  antennas  of,  186. 
Franklin,  Benjamin,  experiments  of,  2. 

Invention  of  torpedo  by,  78. 
Frequency         transformer         (Golcl- 

schmidt),   174. 

Fulton,  Robert,  experiments  by,  with 
torpedoes,  78. 

Gale,  Prof.,  experiments  of,  in  water 
conductivity,  13. 

Galileo,  early  theory  of,  6. 

"Galvanic  excitation"  of  Steinheil,  8. 

"Galvanic  induction  of"  Steinheil,  8. 

Galvanometers,  2. 
As  relays,  182. 

Gardner,  John,  sensitive  vibratory  re- 
lays of,  ii. 
Torpedo  control,  system  of,  93. 

Galvanoscope,  2. 

Gauss,  experiments  of,  2. 


INDEX 


203 


Generator  amplifier,  175. 
Goldschmidt,    Dr.,    frequency   trans- 
former of,  174. 

Goose  quills,  use  of,  for  insulation,  3. 
Gray,  Stephen,  early  discovery  by,  2. 

Hammond,   John   Hays,   Jr.,   experi- 
ments by,  107. 
Steering  apparatus  of,  114. 
Torpedo  control,  system  for  coast 

defence,  122. 
Hammond  radio  research  laboratory, 

work  of;  107. 
Heat,  detectors  of,  10. 
Heliograph,  i. 
Henry,  invention  by,  3. 
Hertzian  waves,  77. 

Branly's  experiments  with,  28. 
Lodge's  experiments  with,  28. 
Hetrodyne     receiver     (Fessenden), 
167,  173,  178. 

Indians,  signalling  by,  i. 

Indicator  currents  in  radio  receivers, 
experiments  of  G.  W.  Pierce  in, 
150. 
Nature  of,  150. 

Induction-conduction    telegraph   sys- 
tems (Preece's),  25. 

Inductive  effects  in  telephone  circuits, 

IS- 
Infra-red  or   heat  waves,   selectivity 

of,  44. 

Use  in  torpedo  control,  41. 
Interference  preventer,  159. 

Of  Fessenden,  142. 

Ion  controller  detector  (Lowenstein), 
24. 

Knauss,   experiments   of,    in   torpedo 
control,  100. 

Leon,  Capt.  K.  O.,  experiments  with 
torpedoes,  199. 


Le  Sage  of  Geneva,  2. 

Electrostatic  telegraph  of,  4. 
Leyden  jar,  discovery  of,  2. 
Light  telephony,  60. 
Lindsay,  James  Bowman,  experiments 

of,  in  water  conductivity,  14. 
Lodge,  Sir  Oliver,  experiments  with 

Hertzian  waves,  28. 
Lowenstein,  amplifier  of,  62. 

Electrostatic  telegraph  of,  23. 
Ion  controller  detector,  24. 

Magnetic  detectors,  171. 
Marconi,  early  experiments  of,  31. 

Law    of,    for    height    of    antennae, 

183- 
Marine  signalling,  Bells  plan  for,  17. 

Method  of  Rathman,  18. 

Method  of  Rubens-,  18. 

Method  of  Strecker,  18. 
Microphonic  amplifier,  175. 
Micro-radiometer  (Weber),  47. 
Monotelephone  amplifier,  141. 
Morse,  foundation  of  overland  system, 

3- 
Development  of  overland  system  of, 

4- 

Sounder  of,  4. 

Experiments   of,    with   earth   con- 
duction, 12. 

Report  of,  to  government,  12. 
"Multipliers"  of  Steinheil,  8. 
Muschenbroek  of  Leyden,  2. 

Nichol's  radiometer,  51. 

Orientation      mechanism     ("  Electric 

Dog"),  194- 

Applied  to  Hammond  dirigible  tor- 
pedo, 197. 
Double,  198. 
Experiments  of  Captain  Leon  with, 

199- 
Oersted,  discovery  by,  2,  4. 


2O4 


INDEX 


Parabolic  reflectors,  42. 

Photophone,  of  Bell  and  Tainter,  9. 

Pierce,  Prof.,  G.  W.,  experiments  of, 
in  indicator  currents  in  radio  re- 
ceivers, 150. 

Pliny,  early  discovery  by,  2. 

Pneumatic  steering  apparatus,  188. 

Potentio  detector,  134. 
Adjustment  of,  135. 

Poppoff  s  receiver,  description  of,  30. 

Preece's  induction-conduction  system, 
description  of,  25. 

Radiant    energy    in    ether    and    air, 

vibration  frequencies  of,  33. 
Radiant  heat  detectors,  46. 

Classification  of,  47. 
Radio  control,  experiments  in  Europe, 

193- 

Recent  developments  in,  188. 
Radiodynamic  torpedo  (Tesla),  85. 
Radiodynamics,  sound  waves  in,  36. 
Radio-Goniometer  (Bellini  and  Tosi), 

44,  140. 

Radiometer,  51. 
Radiomicrometer  of   d'Arsonval  and 

Boys,  51. 

Radio  receivers,  indicator  actions  of, 
163- 

Indicator  currents  in,  150. 
Radiotelegraph,     experiments     with, 

(Austin),  72.     , 
First,  10. 

Power  of  transmitter,  35. 
Range  of  received  power,  35. 
Radio  tower,  common  type  of,  184. 
Rathbone,  Charles,  discovery  by,  14. 
Receivers,     hetrodyne     (Fessenden), 

167,  173,  178. 
Poppoff  s,  30. 
Selective,  137. 

"Whip-crack"  effect  in,  137. 
Receiving  wave  detector,  Varley's  use 
of,  27. 


Rectifiers,  crystal,  172. 

Vacuum  tube  of  De  Forest,  129. 
Reflectors,  parabolic,  42. 
Relay,  capillary  electrometer  as,  182. 

Galvanometer  as,  182. 

Importance  of,  180. 

Improvements  of,  1 26. 

Invention  of,  5. 

Non-polarized,  181. 

Polarized,  181. 

Resonance,  141. 

Sensitive  vibratory,  of  Gardner,  n. 
Resonance  relay,  141. 
Roberts,  dirigible  balloon  of,  86. 
Romagnesi  of  Trent,  discovery  by,  2, 
4- 

Sacher,  Prof.,  E.,  experiments  of,  in 
induction,  15. 

Schilling,  telegraph  of,  2. 

Schweigger,  discovery  by,  2,  4. 

Searchlights,  electric  atmospheric  ab- 
sorption and  dispersion  of  rays, 

45- 

Invisibility  of  rays,  43. 
Selective  receivers,  137. 
Selective     transmitter-receiver     unit, 

145- 

Selectivity,  means  of  obtaining,  145. 
Selectors,  89. 
Branley's,  92. 
Codal,  141. 
Hiilsmeyer's,  93. 
Walter's,  92. 
Self-directing  torpedoes,  194. 

Experiments  of  Capt.   Leon   with, 

199. 
Orientation  mechanism  applied  to, 

199. 

Semaphore  system,  i. 
Signalling,  early  methods,  i. 
Flag,  i. 

Submarine   (Fessenden's  apparatus 
for),  36. 


'INDEX 


205 


SUenium,  57. 

Cells,  57. 

Selectivity  of,  63. 
Sims,  dirigible  torpedo  of,  86. 
Siren  interference  machines,  143. 
Sonorescent   property   of   substances, 

10. 

Sound  waves  in  radiodynamics,  36. 
Sound-relaying  system,  of  Davy,  10. 
Sounder,  electromagnetic,  of  Morse,  4. 
Steering  apparatus  (Hammond),  114. 

Pneumatic,  188. 
Steinheil,  system  of  telegraphy  of,  2. 

Radio-telegraphic  system  of,  10. 

Scheme  of  earth-plates  of,  9. 

Use  of  railway  by,  3. 

Wireless  telegraph  of,  6,  9. 
Sturgeon,  invention  by,  3. 
Submarine   signalling,    Prof.    Fessen- 
den's  apparatus  for,  36,  40. 

Tainter,  Sumner,  photophone  of,  9. 
"Tasimeter,"  Edison's,  10,  52. 
Telautomaton  (Tesla),  84. 
Teledynamics,  development  of,  4,  5. 
Teledynamic  system,  principal  parts 

of,  33- 

Telefuncken,  transmitter  of,  139. 
Telegraph,  automatic  recording,  3. 

Electrostatic,  4-23. 

Electromagnetic,  4. 

First  invented,  2. 

First  overland,  3. 

First  in  U.  S.,  4. 

Needle,  3. 

Wireless,  6,  12. 
Telephone,  inductive  effects  in,  15. 

Invention  of,  14. 

Wireless,  14. 
Telephony,  light,  60. 
Tesla,  Nikola,  early  experiments,  28. 

Invention   of    wirelessly   controlled 
vessel,  83. 

Radiodynamic  torpedo  ot,  85. 


Tesla,  Nikola,  Telautomaton  of,  84. 
Thales,  early  discovery  by,  2. 
Theophrastus,  early  discovery  by,  2. 
Thermal  detectors,  166,  171. 
Thermocouple,  49. 
Thermoelectric  detectors,  48,  171. 
Thermogalvanometer,  Duddell's,  171. 
Thermo-electric  pile,  9. 
Thermopile,  41,  48.        7 

Of  Coblentz,  49. 

And  galvanometer  relay,  51. 
Thermostat,  53. 

Torpedo,   advantages  and   disadvan- 
tages, 83. 

Antennae  of,  183. 

Battle  range,  control  of,  124. 

Coast  defense  (Hammond),  122. 

Control  systems  for,  93,  96,  100. 

Demonstrations    of,    before    U.    S. 
War  dept.,  121. 

Description  of,  79. 

Dirigible,  86,  102. 

Experiments  of  Leon  with,  199. 

First  test  of,  78. 

Invention  of,  78. 

Methods  of  launching,  80. 

Radiodynamic  (Tesla),  85. 

Self-directing,  194. 
Transmitter  of  Telefuncken,  139. 
Trowbridge,    Prof.,    John,    study    of 
electromagnetic  induction  signal- 
ling, 15- 

Ultra-violet  radiations,  64-66. 
Ulivi,    experiments   of,    in    F    Rays, 
193- 

Vacuum-detector,  173. 

rectifier,  of  De  Forest,  129. 
Vacuum-tube,  amplifier,  177. 
Varley's  use  of  receiving  wave  detec- 
tor, 27. 
Vibration     frequencies     of     radiant 

energy  in  ether  and  air,  33. 


206 


INDEX 


Waiter,  codal  selector  of,  141. 
Watson  of  Llandaff,  early  discovery. 

by,  2. 
Wave   systems,   electromagnetic,    27, 

28,31,32. 

Waves,  infra-red,  41,  44. 
Weber,  micro-radiometer  of,  47. 
Wheatstone,  needle  telegraph  of,  3. 
Automatic  recording  telegraph  of, 

3- 

"Whip-crack"  effect  in  receivers,  137. 

Wilkins,  J.  W.,  experiments  of,  with 
earth  conduction,  14. 

Willoughby  Smith,  discovers  proper- 
ties of  silenium,  57. 

Wilson,  Ernest,  invention  by,  of  wire- 
less control  of  vessels,  83. 


Wireless  telegraphy,  6. 
First,  of  Steinheil,  6. 
Later,  of  Steinheil,  9. 
Practical,  12. 

Wireless  transmission  of  energy,  ex- 
periments of  Nikola  Tesla,  28. 
Wireiessly  controlled  vessels,  system 

for  (Wilson),  83. 
Invention  of  (Tesla),  83. 
Description  of,  84. 
Wirth,  codal  selector  of,  141. 

Experiments  of,  in  torpedo  control, 
100,  102. 

Zickler,  Prof.  E.,  use  of  ultra-violet 
rays  in  telegraphy,  65,  66. 


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